19 But if Christ's disciples are unwilling to learn from Christ what veneration and honour is due to the name of the Father, still let them learn from earthly and secular examples, and know that Christ has declared, not without the strongest rebuke, “The children of this world are wiser in their generation than the children of light.” In this world of ours, if any one have offered an insult to the father of any; if in injury and frowardness he have wounded his reputation and his honour by a malevolent tongue, the son is indignant, and wrathful, and with what means he can, strives to avenge his injured father's wrong.
Think you that Christ grants impunity to the impious and profane, and the blasphemers of His Father, and that He puts away their sins in baptism, who it is evident, when baptized, still heap up evil words on the person of the Father, and sin with the unceasing wickedness of a blaspheming tongue? Can a Christian, can a servant of God, either conceive this in his mind, or believe it in faith, or put it forward in discourse? And what will become of the precepts of the divine law, which say, “Honour your father and your mother?” If the name of father, which in man is commanded to be honoured, is violated with impunity in God, what will become of what Christ Himself lays down in the Gospel, and says, “He that curses father or mother, let him die the death;” if He who bids that those who curse their parents after the flesh should be punished and slain, Himself quickens those who revile their heavenly and spiritual Father, and are hostile to the Church, their Mother?
An execrable and detestable thing is actually asserted by some, that He who threatens the man who blasphemes against the Holy Spirit, that he shall be guilty of eternal sin, Himself condescends to sanctify those who blaspheme against God the Father with saving baptism. And now, those who think that they must communicate with such as come to the Church without baptism, do not consider that they are becoming partakers with other men's, yea, with eternal sins, when they admit without baptism those who cannot, except in baptism, put off the sins of their blasphemies.
Source: The Epistles of Cyprian (New Advent)