The Bible teaches that by reason of the Fall, man has become totally incapable of any good and prone to all evil (Gen. 6:5; 8:21; Job 14:4; Isa. 53:6; Jer. 17:9; Jn. 3:6; Rom. 3:9-18; 7:18).
Such truth often finds much resistance within contemporary American Evangelicalism and raises the inevitable objection, “If man is incapable of doing what God requires, doesn’t this make God unjust?”
Is God unjust for requiring man to do that which he cannot do? Isn’t this unfair and doesn’t it make God unmerciful?
No! The Scriptures teach that God made man capable of doing what the Law commands. But through the fall, Adam and all of his descendants lost this capability. Paul, in Romans 5:12 writes, “Therefore, just as sin came into the world through one man, and death through sin, and so death spread to all men because all sinned.”
Man’s inability to keep the Law is not an excuse, it is guilt. No man is forced to sin. On the contrary, man sins voluntarily.
The Heidelberg Catechism (1563), anticipating such an objection, asks and answers:
9. Does not God, then, not do injustice to man by requiring of him in His law that which he cannot perform?
A. No, for God so made man that he could perform it; but man, through the instigation of the devil, in deliberate disobedience deprived himself and all his descendants of this power.
 Gen. 1:31.  Gen. 3:13; John 8:44; I Tim. 2:13, 14.  Gen. 3:6.  Rom. 5:12, 18, 19.
Man’s inability to keep the Law is not an excuse, it is guilt.
The Scriptures validate the just nature of God and the guilt of man. The justness of God is not nullified by the guilt of man. Rather, God manifests His justness by exposing man’s unjustness.
To borrow the Apostle Paul’s words, “Is God unjust? By no means! Let God be true though every man a liar.”