KEY TEXT: Faith must always be seen in the context of a promise: “Abraham believed the Lord” after he was shown the stars in the night-sky as a promise of innumerable descendants through the son of his own body. So faith is not believing in whatever we like (e.g. God will make me happy and successful, no matter what) but faith is belief in the promises of God given in His word or personally through His Spirit. Biblical faith is rooted in scriptural promises--not in our own self-beliefs. We may have strong self-beliefs but as long as they are not from Scripture or the Spirit, we don't have biblical faith: “So then faith comes by hearing, and hearing by the word of God” (Romans 10:17, NKJV).
So, faith is based on a promise God made to us, and when we believe the promise, it is “credited” (NIV) or “counted” (ESV) to us as our righteousness. The reason faith is counted as righteousness is because faith is the foundation to receive all the blessings of God—viz., his life-transforming grace which includes God's own righteousness. So faith receives the gift of God’s righteousness so it becomes our own—God's righteousness is not a loan from God but a gift. In other words, through faith, God’s righteousness has been credited to our account.
An analogy might help. Every year, our government credits into our CPF account our annual GST rebate. It’s not a loan from the government, but a gift. It’s based on a promise the government made to all citizens. We elect the Government because we believe in its ability to deliver on its promise, regardless of whether or not we deserve it.
So now in the NT Gospel: our faith is based on the promise of inheritance of God's eternal kingdom. When we believe God’s promise, we become citizens of God’s kingdom. And as citizens of God's kingdom, Christ’s righteousness is automatically credited into our account because we are members of His kingdom. We don’t deserve it (grace) but we have received it only because we believe in God’s ability to deliver on His promise of eternal life through Christ. Christ’s righteousness is not a loan to us but a gift. And it belongs to us permanently.
Father, thank You for the gift of righteousness because we believe in Your promise in the Gospel. Thank You that we have Christ’s righteousness in us. Help us to live as righteous people, no longer compromising with sin and the flesh. Amen.