John Calvin on Jude 1:2

2. Mercy to you. Mercy means nearly the same as grace in the salutations of Paul. Were any one to wish for a refined distinction, it may be said that grace is properly the effect of mercy; for there is no other reason why God has embraced us in love, but that he pitied our miseries. Love may be understood as that of God towards men, as well as that of men towards one another. As mercy is that of God, so it is more consistent to consider “peace” and “love’’ to be those of God: “may the mercy” of God, “and the peace” of God, “and the love” of God, “be increased (or multiplied) to you” — Ed. If it be referred to God, the meaning is, that it might increase towards them, and that the assurance of divine love might be daily more confirmed in their hearts. The other meaning is, however, not unsuitable, that God would kindle and confirm in them mutual love.

Jude 3-4

3. Beloved, when I gave all diligence to write unto you of the common salvation, it was needful for me to write unto you, and exhort you, that ye should earnestly contend for the faith which was once delivered unto the saints.

3. Dilecti, quum omne studium adhiberem ad scribendum vobis de communi salute, necesse habui scribere vobis ad vos hortandos ut certando adjuvetis eam, quae semel tradita est sanctis, fidem.

4. For there are certain men crept in unawares, who were before of old ordained to this condemnation, ungodly men, turning the grace of our God into lasciviousness, and denying the only Lord God, and our Lord Jesus Christ.

4. Subingressi enim sunt quidam homines, olim praescripti judicium, impii, Dei nostri gratiam transferentes in lasciviam, et Deum, qui solus est Herus, et Dominum Jesum Christum negantes.