The prophet Isaiah in the context of the return of the chosen people to the promised land, after the exile in Babylon, reminds us that God's providence is generous but that providence depends on the freedom of man: "But your iniquities have separated you from God; your sins have hidden his face from you, so that he will not hear", Isaiah 59:2
This teaching of the prophet Isaiah has a universal scope, evil separates us from the truth, the origin of sin in man is concupiscence: "When tempted, no one should say, "God is tempting me". For God cannot be tempted by evil, nor does he tempted anyone; but each person is tempted when they are dragged away by their own evil desire and enticed. Then, after desire has conceived, it gives birth to sin; and sin, when it is full-grown, gives birth to death". James 1:13-15
The man who sins cannot perceive God: "The natural man does not accept the things that come from the spirit of God, for they are foolishness to him, and he cannot understand them, because they are spiritually discerned." 1 Corinthians 2:14. In other words, human reason affected by disordered desires cannot reach the perception of eternal and immanent truths.
This is why the gift of conversion is necessary according to the scriptures. Conversion is the passage from a life full of sins to a life of righteousness ( "Do unto others as you would have them do unto you", Matthew 7:12). When Jesus begins the preaching the good news he says: "Repent, for the kingdom of heaven has come near", Matthew 4:17. Jesus asks us to turn our face towards God: "Come near to God and he will come near to you. Wash your hands, you sinners, and purify your hearts, you double-minded.", James 4:8
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