2 Thessalonians 2:13 ESV
But we ought always to give thanks to God for you, brothers beloved by the Lord, because God chose you as the firstfruits to be saved, through sanctification by the Spirit and belief in the truth."
We are chosen because we believe. All who choose God will be chosen by Him for salvation. We are made holy by that belief, sealed by the Holy Spirit into the body of Christ as the firs firstfruits of those being saved.
The full crop is yet to be harvested.