Heidelberg Q. 20. Are all men, then, saved by Christ just as they perished through Adam?
A. No. Only those are saved who by a true faith are grafted into Christ and accept all His benefits.

Heidelberg Q. 21. What is true faith?
A. True faith is a sure knowledge whereby I accept as true all that God has revealed to us in His Word. At the same time it is a firm confidence that not only to others, but also to me, God has granted forgiveness of sins, everlasting righteousness, and salvation, out of mere grace, only for the sake of Christ's merits. This faith the Holy Spirit works in my heart by the gospel.