Romans 4:4-5 (NIV)
Now when a man works, his wages are not credited to him as a gift, but as an obligation. However, to the man who does not work but trusts God who justifies the wicked, his faith is credited as righteousness.
Paul makes this oft forgotten concept clear. If there were anything that we could do to merit eternal life from God, then no matter how small a thing we did, God would be paying us back. God owes no man anything. What he offers is given freely. If I were to offer you a gift, you do not have that gift until you reach out with your arms and take it. That is what faith is, the reaching out part. How can that ever be considered a work? It is an effort. It is an act of the will. You could refuse the gift. It is your choice. It is not my will that you refuse the gift; I offered it to you. I would be disappointed in your refusal but I can't make you choose it.
Take a look at the accounting terminology Paul uses in this verse. Faith is credited as righteousness. God is the bookkeeper. He puts righteousness on your account. Does that make you righteous? Many have this idea that there is a set of scales in heaven where God weighs the good that you do against the bad and if the good tips the scales then you get in. The Bible says that even "our righteousness acts are filthy rags in his sight." [Jer 17:9] The transaction Paul describes is not a running account where we are waiting till checkout time to pay the bill. No, the bill is paid in full when you accept the gift. You might ask "what about the sins I commit afterwards?" How many of your sins were yet future when Jesus died on the cross? All of them. God is not surprised when you sin. He already can see all of your future sins. When he stamps "Paid in full" on your bill, the ledger is already completed.
I've got a big grin on my face as I write this.
2 Corinthians 9:15 (NIV)
Thanks be to God for His indescribable gift!