Remember, then, that you received a spiritual seal, the spirit of wisdom and understanding, the spirit of knowledge and reverence, the spirit of holy fear. Keep safe what you received. God the Father sealed you, Christ the Lord strengthened you and sent the Spirit into your hearts as the pledge of what is to come.
AmbroseThe Church was redeemed at the price of Christ's blood. Jew or Greek, it makes no difference; but if he has believed, he must circumcise himself from his sins [in baptism (Col. 2:11-12)] so that he can be saved . . . for no one ascends into the kingdom of heaven except through the sacrament of baptism . . . "Unless a man be born again of water and the Holy Spirit, he cannot enter the kingdom of God"
Ambrose