First, its newness notwithstanding, it was the right idea at the right time. Global mission has had its successes and its failures. The human spirit being what it is, we try to find out what we are doing right so we can repeat the good behavior and try to diagnose the wrong so we can root it out. Contextualization in mission was the rooting out of the bad idea that all western missionaries had to do to be successful was transplant our forms of biblical interpretation, worship, moral codes, standards, and behaviors into the host culture. This cultural imperialism has had devastating consequences in some contexts, but not all. Taking the context of the host culture into account has been a godsend revelation to mission studies and helpful in limiting the harmful aspects of our gospel sharing across cultures.
The second reason for a missiological focus on contextualization is its inherent truth in the operations of God. The doctrine of the incarnation is as old as John's gospel when he wrote, "In the beginning was the Word, and the Word was with God, and the Word was God. . . . And the Word became flesh, and dwelt among us, and we saw His glory, glory as of the only begotten from the Father, full of grace and truth" (v 1, 14). I have learned in seminary before that this was the Holy God, who is completely other than what we are and fully apart from us as spirit, that condescends to us in our humanity to show us His face and, thereby, save us from ourselves. I have understood this doctrine for many, many years and yet it took on a fuller meaning when I was in class with my Korean missionary friends.
What God did in the incarnation, among many things, is that He entered a middle-Eastern, 1st century Jewish context and demonstrated to us all--even those of us 20 centuries removed from this appearing--that this is the way of God. He left his context as the wholly and holy other God and entered our context, the broken, fallen existence of those He created and loved to win us to Himself. And, not only did he enter human existence as both God and human, but he entered it as a baby, born to a teenage Jewish girl, in the collision of multiple cultures . . . Judaism, Greek, and Roman. He showed us the ultimate way of contextualization, of entering another's context, by leaving his place in heaven to be with us, in our culture, in full vulnerability. This is the reason why contextualization in mission is so invigorating to those who think and write for a living. It is so much the truth, the truth of how God works in human lives, that it startled many academics into wondering how we failed to fully understand the incarnation until we first failed at modern mission and then discovered it is because we didn't follow Christ's example.