The Greek word for hearts conveys this meaning: as the seat of feelings, desires, joy, pain, and love. It is also the center for thought, understanding, and will. (copied from note in my Bible). Our heart is our belief center, and also where the Holy Spirit dwells.

David’s prayer in Psalm 26:3 was giving the Lord permission to probe. It says, “Examine me, O Lord, and prove me; try my mind and my heart.” The Hebrew word for try means any refining, whether literal or figurative; to try by fire.

In Revelation 3:14 He counseled the Laodicean church, “…to buy from Me gold refined in the fire…” Think back to 1 Peter 1:7. Our trials purify our faith. That church viewed themselves through their own eyes as needing nothing. They acted independent of God and were fruitless. John 15:5. The Lord saw their hearts that were blinded through deception.