Baptism was instituted for a sign that a man is of the church, and for a memorial that he must be regenerated; for the washing of Baptism is no other than spiritual washing, or regeneration.
All regeneration is effected by the Lord, by means of the truths of faith and a life according to them. Baptism therefore testifies that a man is of the church, and that he can be regenerated. For in the church the Lord is acknowledged, who alone regenerates; and there the Word is, wherein are the truths of faith by which regeneration is effected.
The Lord thus teaches in John:—"Except a man be born of water and of the Spirit he cannot enter into the kingdom of God." In the spiritual sense water is the truth of faith from the Word; the spirit is life according to it; and to be born of them is to be regenerated by them.
Since every one who is regenerated also endures temptations, which are spiritual combats against evils and falsities, therefore these also are signified by the waters of baptism.
Because baptism is for a sign and a memorial of these things, a man may be baptized as an infant; and if not then, he may be as an adult.
Those who are baptized should therefore know that the Baptism itself confers neither faith nor salvation; but testifies that they may receive faith, and that they may be saved if they are regenerated.
From this it is evident what is meant by the Lord's words in Mark:—"He that believeth and is baptized shall he saved; but he that believeth not shall be condemned" (ch. xvi. 16). He that believeth is he who acknowledges the Lord and receives truths from Him through the Word; he that is baptized is he who is regenerated by means of them by the Lord. (H. D. n. 202-208.)
That baptism was commanded is very manifest from the baptism of John, in the Jordan, to which there went out all Judea