The theme of the Holy Father's Lenten Message this year is 'The Justice of God'; and I urge you to read it here.
His Holiness makes the point that 'Conversion to Christ, believing in the Gospel, ultimately means this: to exit the illusion of self-sufficiency in order to discover and accept one’s own need – the need of others and God, the need of His forgiveness and His friendship'.
There can be nothing that more clearly emphasizes our inability to be self-sufficient than the Cross : for nothing we could do could ever have paid the debt due to God as a result of Original Sin - only Christ, the Son of God, could do that; and He did.
Let us, during this Lent now so close at hand, consider the Holy Father's words, and recognize our own inability to achieve anything without His grace - grace which is 'a gift, through the redemption which is in Christ Jesus, whom God put forward as an expiation by His blood, to be received by faith'. (Romans 3, 24-25)