Jude 1:20

building up yourselves on your most holy faith Both the adjective, which is nowhere used of faith in its subjective sense, and St Jude's use of the substantive in Jude 1:3, lead us to take "faith" in the objective sense, as nearly identical with "creed," which attaches to it in the later Epistles of the New Testament (1 Timothy 5:8 and perhaps 2 Timothy 4:7). The readers of the Epistle are exhorted to take that faith as a foundation, and to erect on it the superstructure of a pure and holy life.

praying in the Holy Ghost The precise combination is not found elsewhere in the New Testament, but the fact which it expresses corresponds with St Paul's language in Romans 8:26, and the almost identical phraseology of 1 Corinthians 14:15. What is meant is the ecstatic outpouring of prayer in which the words of the worshipper seem to come as from the Spirit who "helpeth our infirmities" and "maketh intercession for us," it may be in articulate speech, it may be also as with "groanings that cannot be uttered" (Romans 8:26). Here again we may recognise a side-glance at the false teachers. Not those who deserted the Church's faith for a life of impurity, but those who "built" on it a life of holiness, were capable of that height of devotion which is described as "praying in the Spirit."