Be baptized: believing and making profession to believe, and hope for salvation, by the merits of Jesus Christ. Thus you shall receive the gift of the Holy Spirit, the grace of God, and perhaps those other gifts of speaking with tongues, working miracles (Witham)
The gift of the Holy Spirit. That is, justifying grace, which is infused in our hearts by the laver of regeneration. The exterior gifts of the Holy Spirit, the gift of tongues, of miracles, prophecy were, in the beginning of the Church, more regularly the consequences of confirmation or imposition of hands. (Calmet)
For, being about to speak of baptism, he spoke first of the lamentations of penitence; that they should first bathe themselves in the water of their own affliction, and afterwards wash themselves in the Sacrament of Baptism. With what conscience, then, can those who neglect to weep for their past misdeeds live secure of pardon, when (Peter) himself believed that penitence must be added even to this Sacrament which chiefly extinguishes sins?
He had admonished men to do penance before admonishing them to be baptized, this would be because also before Baptism some kind of penance is required. Confession is a part of sacramental Penance, which is not required before Baptism, but the inward virtue of Penance is required. Moreover, the penance which precedes Baptism is not the sacrament of Penance.
And you shall receive the gift of the Holy Spirit:
the sacrament of confirmation unto renovation: ‘By the laver of regeneration and renovation of the Holy Spirit’ (Titus. 3:5). For in confirmation the Holy Spirit is given for strength to enable a man to boldly confess Christ’s name before men. For just as in the natural order a man is first born and then grows and becomes strong, so, too, in the order of grace. Hence Pope Melchiades says: "The Holy Spirit, Who comes down on the waters of Baptism bearing salvation in His flight, bestows at the font, the fulness of innocence; but in Confirmation He confers an increase ...