Why does God search the believer's heart through the Holy Spirit?
The Holy Spirit indwells the believer, and through that indwelling Spirit God searches the heart. This is because the Holy Spirit intercedes for the saints according to the will of God, making intercession on their behalf to the Son, who then intercedes to the Father. All three persons of the Godhead are involved.
Les explains that the Holy Spirit, the third person of the Trinity, indwells the believer. It is through that indwelling Holy Spirit that God searches the believer's heart, because the Holy Spirit makes intercession for the saints according to the will of God. The Spirit intercedes on our behalf to the Son, and the Son intercedes on our behalf to the Father. Les notes this involves all three persons of the Godhead and is a concept we accept by faith. He then connects this to verse 28, where all things work together for good, but only for the believer, not the world. Les shares that even hard experiences ultimately work for the believer's good.