St. Ambrose: “But I hear that you grieve because he did not receive the sacrament of baptism.....
"The reason these faithful were grieved was because they believed that "unless a man be born again of water and the Holy Ghost he cannot enter the Kingdom of God."
Perhaps too,
they had been Instructed by Ambrose himself, who said: 'One is the Baptism which the Church administers: the Baptism of water and the Holy Ghost, with which catechumens need to be baptized . . . Nor does the mystery of regeneration exist at all without water: 'For unless a man be born again of water and the Spirit, he cannot enter into the kingdom.' Now, even the catechumen believes in the cross of the Lord Jesus, with which he also signs himself; but, unless he be baptized in the name of the Father, and of the Son, and of the Holy Ghost, he cannot receive remission of his sins nor the gift of spiritual grace." (De Mysterlls,-THE DIVINE OFFICE)". - From Who Shall Ascend?