We learn this through the enlightenment of the Holy Spirit.
210. What is meant by the enlightenment of the Holy Spirit?
Through the enlightenment of the Holy Spirit our knowledge of the Gospel truths becomes a living and saving knowledge to our hearts.
John 14:26. But the Comforter, the Holy Ghost, whom the Father will send in my name, he shall teach you all things, and bring all things to your remembrance, whatsoever I have said unto you.
John 16:13. When he, the Spirit of truth, is come, he will guide you into all truth.
211. Of what nature is our knowledge of these truths before the Holy Spirit has enlightened our hearts?
It is a dead knowledge only, which does not lead to repentance and faith, but leaves us in our sins.
212. What is the true and living faith in Jesus Christ?
This is faith, that a repentant sinner lays hold of Christ as his only Savior from sin, and death, and the power of Satan;