E.V. Gerhart argues in his 1873 Mercersburg Review article that the Heidelberg Catechism teaches that “Baptism makes the sinner a new man.”
He explains: “The word ‘renewed’ in this connection . . . is to be taken as affirming a new organic relation of the subject of Baptism with Christ, the Head of His mystical body. It means that we are made partakers of His life.” This is evident from the fact that the Catechism connects this renewal with being “sanctified to be members of Christ,” and explains that “the subject of Baptism is both renewed and sanctified by the Holy Ghost. The Spirit renews him, and in renewing him, sanctifies him. The Spirit sanctifies him, but He sanctifies him in that He makes him really a new man. The new position which he occupies as renewed and sanctified by the Spirit, the Catechism expresses by the phrase: ‘members of Christ.’ The subject becomes by Baptism a member of Christ” (544-5).
Becoming a member of Christ isn’t a goal reached by “improving the grace of baptism.” We are made members of Christ by renewal and sanctification, “and this renewing and sanctifying work of the Spirit is the mystical washing of Holy Baptism” (545).
Prior to baptism, we are in Adam. That is “our position and character by nature.” But “the Spirit takes us out of our natural position and translates us into a spiritual position.” By virtue of this new relation and position, we are live a new and holy life, but the renewal and sanctification are the starting point, worked by the Spirit, in the “mystical washing of Baptism” (546).