Why do you believe it is so important to understand that, in regards to salvation, God chose us first?

Because God means to get all the glory for our salvation. We need to know the One on whom we're leaning and what we're really leaning on him for. Let me say a word about each of these two things.

The second one: we need to know how we got saved. We were born not of blood, not of man, not of the human will--we were born of God. That is, we were brought into being as spiritually alive people by God. We were dead, according to Ephesians 2, and now we are alive together with God--by grace we have been saved.

Grace is the sovereign work by which God speaks to the dead corpse of our own spiritual life, and says, "Lazarus, come forth," and we awake from the dead, or "John Piper, come forth!," and we are brought into being. We need to know that so that we can rest in God's sovereign saving of us. That's how we got saved! We didn't somehow raise ourselves from the dead. We didn't somehow create--out of nothing--spiritual affections. God did this for us, which leads now to the first thing: he means to be glorified for all of this.

God wants to be acknowledged for all that he has done and for all that he is. We will not give him all of the praise and glory that he should get if we don't acknowledge what he has done for us. So I think it is really important that we teach people how they actually got saved, even if they don't fully understand how they got saved, because we want them to begin--now better than never--praising and honoring and relying on God for all that he did and not just for part of it.