Help for the listless sinner, who wonders if all the effort and trouble is worth it. yes! Yes it is. God justifies the ungodly. Stop working! Trust. Get up, pray, read the Bible, go and enjoy nature. It's there and it shouts His name. The name of the one who stands ever between you and the Father.
Help for the fallen saint, who can't bare to turn to see their Father frowning at them, who can't face the Lord in prayer with the taunts of the enemy in his ear. Incredibly, because of the cross, the Lord will plead your cause, He will execute judgement for you. For you. So 'fess up. Trust Christ to the hilt with gutsy guilt. Look at the cross and wonder, and sin no more.
Help for the squeamish fellow, who doesn't know whether he can call all the world, all the languages, all the ethnicities, all the differences to one Savior. Who doesn't know if Jesus is important enough for all the nations, who is embarrassed at the claims that all those needs can be wonderfully met by one man. Christ is the second Adam. As the first bought unrighteousness for all, so the second buys righteousness for all. Rejoice!
Isn't that the shame of the penal substitution deniers? That denying penal substitution denies us this Christ exalting, broken, mission mobilising joy?