Heidelberg Catechism - Lord's Day 23

59. Q . What good does it do you, however, to believe all this?
      A. In Christ I am righteous before God and heir to life everlasting.

60. Q . How are you righteous before God?
      A. Only by true faith in Jesus Christ.
Even though my conscience accuses me of having grievously sinned against all God’s commandments, of never having kept any of them, and of still being inclined toward all evil, nevertheless, without any merit of my own, out of sheer grace, God grants and credits to me the perfect satisfaction, righteousness, and holiness of Christ, as if I had never sinned nor been a sinner, and as if I had been as perfectly obedient as Christ was obedient for me.
All I need to do is accept this gift with a believing heart.

61. Q . Why do you say that through faith alone you are righteous?
     A. Not because I please God by the worthiness of my faith. It is because only Christ’s satisfaction, righteousness, and holiness make me righteous before God, and because I can accept this righteousness and make it mine in no other way than through faith.