Why do we need to keep coming back to the truth that God opens our hearts?
We keep returning because Satan and the principalities and powers oppose believers and keep lost humanity in darkness until God breaks their authority. God alone opens hearts and through the Holy Spirit gives understanding. Reminding ourselves of this keeps us dependent on His work rather than flesh.
Les explains that Paul's warning in Ephesians is that we wrestle not against flesh and blood but against principalities and powers whose authority is Satan. Satan works to frustrate the life of believers and to keep lost humanity in darkness, and he has that power until God breaks it. That is why, again and again, we must come back to the very fact that God is the One who opens our hearts and, through the working of the Holy Spirit, gives us understanding. Les then points to Romans 8, where neither principalities, nor powers, nor things present, nor things to come, nor height, nor depth, nor any other creature can separate us from the love of God which is in Christ Jesus.