Paul says that God “chose us in him” to emphasize that salvation depends totally on God. We are not saved because we deserve it, but because God is gracious and freely gives salvation. We did not influence God’s decision to save us; he saved us according to his plan. Thus there is no way to take credit for our salvation or to allow room for pride. The mystery of salvation originated in the timeless mind of God long before we existed. It is hard to understand how God could accept us. But because of Christ, we are holy and blameless in his sight. God chose us, and when we belong to him through Jesus Christ, God looks at us as if we had never sinned. All we can do is express our thanks for his wonderful love.
Taken from NIV Life Application Study Bible