What is the defining characteristic of God? Most people throughout history would have answered immediately, "Power." God is set apart from us because he can do things that we cannot do. The Bible certainly agrees that God has power, but this is not the definition of what it means to be God. Orthodox Christian theology teaches that Jesus did not cease to be God even though he surrendered the independent exercise of his power, and was weak as we are. While we may shy away from the implications, the incarnation showed us something remarkable and unexpected about God that we never would have understood any other way: that power is not the essence of divinity. Of course, this statement is derived from later trinitarian formulas, not the New Testament; what does the Scripture itself say?
Probably the clearest answer comes from Philippians 2:5-11 (a passage which figured prominently in the formation of trinitarian theology). Here is this short poem in its entirety (NRSV translation):
3Do nothing from selfish ambition of conceit, but in humility regard others as better than yourselves. 4Let each one of you look not to your own interests, but to the interests of others. 5Let the same mind be in you that was in Christ Jesus,Paul says that Jesus was "in the form of God" (v. 6) and it is hard not to take this in the same sense that Plato used the word "form", meaning that Jesus is the eternal, perfect ideal of God. (There is some debate about whether we can attribute a Platonic sense to "form" here, but Paul says pretty much exactly that Jesus is the ideal of God later in this passage, so I see no reason not to interpret the phrase that way here.)
6who, though he was in the form of God,
did not regard equality with God as something to be exploited,
7but emptied himself,
taking the form of a slave,
being born in human likeness.
And being found in human form,
8he humbled himself
and became obedient to the point of death--
even death on a cross.
9Therefore God also highly exalted him
and gave him the name that is above every name,
10so that at the name of Jesus
every knee should bend
in heaven and on earth and under the earth,
11and every tongue confess
that Jesus Christ is Lord,
to the glory of God the Father.
Perhaps the key phrase here is what is translated by the NRSV "did not consider equality with God something to be exploited" in v. 6. Most older translations have something slightly different (KJV "thought it not robbery to be equal with God"; NIV, NAS "did not consider equality with God something to be grasped"). The reason for the diversity is that a key Greek word, harpagmon, occurs only here in the New Testament, and in the writings of the church fathers only when discussing this passage, so its meaning was not clear. More recent philological research (see references in the article by Wright cited below) indicates than harpagmon means something to be exploited rather than something to be grasped or seized or held on to. "Something to be exploited" makes much better sense of the passage. Jesus possessed equality with God (he did not have to grasp for it)--but he did not exploit that for selfish ends.
Instead, Jesus did nothing from selfish ambition or conceit and regarded others as better than himself--that is the implication of v. 3, since we are to be that way in imitation of him. The whole Roman world was devoted to doing things to gain honor, more so than our culture; it is hard for us to understand the extravagant lengths people in a shame-based culture go to gain honor for themselves. Honor in such a society tends to be like a currency: if you gain it, someone else loses it, and that's how politics and just about everything else was played out in all the cultures around the Mediterranean world. Striving for honor in that culture, perhaps more than in our own, meant putting down other people, the opposite of "being in full accord and of one mind". The ultimate honor, of course, was payed to the gods, who were as jealous of their praise as any human would be.
But Jesus was not like that: Jesus did not consider equality with God something to be exploited to gain honor and praise, unlike, for example, the Roman emperors who even at this time were beginning to be worshiped in the eastern parts of the empire as gods. What did Jesus consider equality with God to mean? Jesus thought equality with God meant emptying himself for us.
Instead of demanding reverence and homage as God, he humbled himself and took on the form of a human. More than that, he humbled himself further to the point of death on a cross. Crucifixion was not only a painful way to die; it was the most humiliating death possible, designed to take every last vestige of honor from the victim; and that's why the Romans did it. (Remember that taking honor from someone else, it was thought, would bring you honor; in our culture, which has lived in the shadow of the cross for a millenium and a half, such actions might discredit you rather than bring you honor, but people did not think that way in the ancient world, or even in some cultures in the modern world.) Victims were nailed to a cross naked, in full view of everyone. This was usually done at the gates to cities, where as many people as possible would pass by, to show their absolute powerlessness to avoid even the most agonizing of suffering, and thereby to glorify the conqueror.
The poem says several times that Jesus took on the form of a slave, or servant. On its own, the Greek is probably better translated "slave", but "servant" correctly alludes to the Old Testament figure called the "Servant of Yahweh". The Servant of Yahweh endures humiliation, and everyone around him thinks that it is for his own sins (Isaiah 52:12-53); but this is not so. He suffers out of obedience to Yahweh, because it was necessary for redemption of the people. Following the outline of Isaiah's climactic poem on the work of the Servant (Is. 53), the text in Phillipians also shows how God highly honored the Servant for his obedience.
God did not have the same opinion as people. "Therefore God also highly exalted him, and gave him the name above every name...." To a Jew like Paul, there is only one "name above every name": the tetragrammaton YHWH, "Yahweh", "I am who I am". Because of his obedience as a servant, and his humility for our sake, God points to Jesus and says, "This is who Yahweh is. This is what it means to be Yahweh."
Lest we miss the idea that Jesus in his humiliation for us is the truest possible vision of Yahweh, he goes on to quote unmistakably from one of the most monotheistic passages in the Old Testament about Yahweh (Isaiah 45:23). In its context, it is part of a challenge to the Babylonian gods to present evidence, any evidence at all, that they can save:
21Who told this [that Cyrus the Great would conquer] long ago?
Who declared it of old?
Was it not I, Yahweh?
There is no other god besides me,
a righteous God and Savior;
there is no one besides me.
22Turn to me and be saved,
all the ends of the earth!
For I am God, and there is no other.
23By myself I have sworn,
from my mouth has gone forth in righteousness
a word that shall not return [void]:
"To me every knee shall bow,
every tongue shall swear."
24Only in Yahweh, it shall be said of me,
are righteousness and strength;
all who were incensed against him
shall come to him and be ashamed.
Referring to this passage, Paul says, "At the name of Jesus, every knee shall bow, and every tongue confess that Jesus is Lord, to the glory of God the Father." The passage from Isaiah was speaking of men confessing Yahweh to be the true God; Paul has taken this and changed in into a confession that "Jesus is Lord." "Lord" is an ambiguous word in Greek. It can mean a polite "Sir"; it can mean "Master" or "Caesar"; or it can mean Yahweh (it is the translation into Greek of "Yahweh" in the Old Testament). Given the context, it seems clear here that "Jesus is Lord" means here that "Jesus is Yahweh." Everyone will eventually confess that Jesus in his humility is exactly what Yahweh God is like.
This confession is "to the glory of God the Father." How does the greatness of Jesus glorify God the Father? Because understanding that Jesus is Yahweh shows us what God the Father is really like: he is just like Jesus, not proud, willing to endure anything for the redemption of those he loves. The greatest glory of God is not primarily in his power, it is in the love that he shows, and Jesus is the ultimate proof of that.
This is not an entirely new idea in the Bible. Moses had seen the incredible power of God in the exodus, but then he prayed to see the glory of God. What did God show him? "Yahweh passed before him and proclaimed, 'Yahweh, Yahweh, a God merciful and gracious, slow to anger, and abounding in steadfast love and faithfulness....'" (Exodus 34:6) The power of God is glorious; but the greatest glory of God is in redemption, in his love and forgiveness.
Other places in the New Testament affirm that the glory of God is found in his love and humility, not primarily in his power. This is particularly evident in the writings of John, where perhaps the most frequently emphasized idea in the gospel is that Jesus reveals the Father by his actions. This is first developed explicitly in John 5:19-20: "The Son can do nothing on his own, but only what he sees the Father doing; for whatever the Father does, the Son does likewise. The Father loves the Son, and shows him everything that he himself is doing...." In the context there, Jesus sees that the Father is raising the dead, so he raises a dead man (metaphorically at that point, literally later); in the next chapter, Jesus sees that the Father is providing spiritual bread, so Jesus provides physical bread; later Jesus sees that the Father is opening the eyes of the blind, so he does it too. Everything Jesus does is an imitation of his Father.
Jesus' imitation of his Father does not stop after his last sign. "Jesus, knowing that the Father had given all things into his hands, and that he had come from God and was going to God, got up from the table, took off his outer robe, and tied a towel around himself. Then he poured water into a basin and began to wash the disciples' feet, and to wipe them with the towel that was tied around him." (John 13:3-5) Washing feet was about the lowest of jobs that could be given to a slave. A Rabbi's disciples would do many menial tasks for him, but they were explicitly not required to wash his feet. Here the Rabbi, knowing his divine origin and destiny, washes his disciples' feet.
What does this say about God? God the Father acts as a servant, just like the best of human parents. After all, Paul says, all fatherhood derives its name from its archetype, God the true Father, Eph. 3:15. A good human parent humbles himself to clean the baby's diapers, and God the Father will do no less for his children. We need that kind of humble service from God, and God is not averse to providing it.
This was not very easily visible before the incarnation, though the Old Testament hints in that direction. For example, Hosea shows God to be suffering and humble (only a humble person can forgive the insult of adultery and accept his erring wife back). But the incarnation has shown much more clearly what God is really like.
In John's first epistle, he twice makes a remarkable statement about the nature of God: "God is love." (1 John 4:8,16) The one thing that we have to understand about God, before anything else, is that the essence of God's nature is love. Pride, arrogance, vengefulness--anything that conflicts with this fundamental part of God's nature is excluded. John says that if you do not understand that about God, you do not know God--you have missed the most important fact about the being of God.
Now the point of the passage in Phillipians, as well as the footwashing passage in the gospel of John and the "God is love" statement in his epistle, is that we are to think the same way: we are to have the same mind in us as was in Christ, and we are to wash each other's feet. We, who are made in the image of God, ought to behave as God did. Unlike Adam and Eve, who sought to be like God to enhance themselves, we are to seek to be like God in that we empty ourselves for others. Jesus, the one who was not only God but also fully human, has showed us the way of true humanity; we are "being renewed in knowledge according to the image of our creator" (Col. 3:10).
A detailed relatively recent discussion of the philology and the theological significance of the Phillipians passage is "Jesus Christ is Lord: Philippians 2.5-11" in The Climax of the Covenant by N.T. Wright.
I first understood this from a really excellent sermon by Darrell Johnson, then at Glendale Presbyterian church a number of years ago, but I have been unable to find any links to anything he has written or spoken on this.