How could Cornelius be righteous if all of man’s righteousness are filthy rags before God?

Answer:

"For from days of old they have not heard or perceived by ear, nor has the eye seen a God besides You, Who acts in behalf of the one who waits for Him. You meet him who rejoices in doing righteousness, Who remembers You in Your ways. Behold, You were angry, for we sinned, we continued in them a long time; and shall we be saved? For all of us have become like one who is unclean, and all our righteous deeds are like a filthy garment; and all of us wither like a leaf, and our iniquities, like the wind, take us away. There is no one who calls on Your name, who arouses himself to take hold of You; For You have hidden Your face from us and have delivered us into the power of our iniquities. But now, O LORD, You are our Father, we are the clay, and You our potter; and all of us are the work of Your hand. Do not be angry beyond measure, O LORD, nor remember iniquity forever; behold, look now, all of us are Your people" (Isaiah 64:4-9).

In contrast to God's holiness, all of us come out looking like we are wearing filthy rages because of our sins. Our righteousness is not much, which is why we note that God has never owed anyone salvation. We could not earn it with the lives we live.

"More than that, I count all things to be loss in view of the surpassing value of knowing Christ Jesus my Lord, for whom I have suffered the loss of all things, and count them but rubbish so that I may gain Christ, and may be found in Him, not having a righteousness of my own derived from the Law, but that which is through faith in Christ, the righteousness which comes from God on the basis of faith, that I may know Him and the power of His resurrection and the fellowship of His sufferings, being conformed to His death; in order that I may attain to the resurrection from the dead" (Philippians 3:8-11).

Left on our own, none of us could be saved. That is why Jesus stepped in. When we obey God in faith, then it is not our own righteousness that we are doing, but we are working the works of God. "For we are His workmanship, created in Christ Jesus for good works, which God prepared beforehand that we should walk in them" (Ephesians 2:10).

When Isaiah saw a vision of God in Isaiah 6, Isaiah was terrified because he realized how inadequate he was to appear before the Creator. "So I said: "Woe is me, for I am undone! Because I am a man of unclean lips, and I dwell in the midst of a people of unclean lips; for my eyes have seen the King, the LORD of hosts" (Isaiah 6:5). But God wasn't interested in Isaiah's self-evaluation. He had a task for Isaiah to accomplish.

Though Abraham sinned, like any other man, his faith, demonstrated through his obedience, was counted as righteousness (Genesis 15:6). That is what matters: having a faith that causes you to do the Lord's will. Paul asked, "Therefore, if an uncircumcised man keeps the righteous requirements of the law, will not his uncircumcision be counted as circumcision?" (Romans 2:26). Thus, "Now there was a man at Caesarea named Cornelius, a centurion of what was called the Italian cohort, a devout man and one who feared God with all his household, and gave many alms to the Jewish people and prayed to God continually. About the ninth hour of the day he clearly saw in a vision an angel of God who had just come in and said to him, "Cornelius!" And fixing his gaze on him and being much alarmed, he said, "What is it, Lord?" And he said to him, "Your prayers and alms have ascended as a memorial before God" (Acts 10:1-4). Because Cornelius, though not a Jew, was living in accordance with God's teachings, God took note of him. Peter later said, "I most certainly understand now that God is not one to show partiality, but in every nation the man who fears Him and does what is right is welcome to Him" (Acts 10:34-35). While Cornelius was a good man, who feared God, he still was a sinner and wasn't saved until he did as God directed (Acts 10:47-48).