Why did Achebe choose to take the title of his novel from Yeats' poem?

"The Second Coming" alludes to the second coming of Christ.  In the poem, this second coming of Jesus is seen as a chaotic event that rocks the world.  In Things Fall Apart, the missionaries are bringing the church's message of Christ, and it's this very message that begins to tear the tribe apart.  It not only pulls away members of the tribe, but it questions and contradicts the very foundations of the tribal belief system.