But ye, beloved, building up yourselves on your most holy faith, praying in the Holy Ghost,

People's New Testament

Jude 1:20 Building up yourselves on your most holy faith. Instead of separating from the faith.

Praying by the Holy Spirit. See PNT Eph 6:18.

Wesley's Notes

1:20 But ye, beloved, not separating, but building yourselves up in your most holy faith - Than which none can be more holy in itself, or more conducive to the most refined and exalted holiness. Praying through the Holy Spirit - Who alone is able to build you up, as he alone laid the foundation. In this and the following verse St. Jude mentions the Father, Son, and Spirit, together with faith, love, and hope.

Jamieson-Fausset-Brown Bible Commentary

20. Resuming Jude 17.

building up yourselves-the opposite to the "separate themselves" (Jude 19): as "in the Holy Ghost" is opposed to "having not the Spirit."

on-as on a foundation. Building on THE FAITH is equivalent to building on Christ, the object of faith.

praying in the Holy Ghost-(Ro 8:26; Eph 6:18). The Holy Spirit teaches what we are to pray for, and how. None can pray aright save by being in the Spirit, that is, in the element of His influence. Chrysostom states that, among the charisms bestowed at the beginning of the New Testament dispensation, was the gift of prayer, bestowed on someone who prayed in the name of the rest, and taught others to pray. Moreover, their prayers so conceived and often used, were received and preserved among Christians, and out of them forms of prayer were framed. Such is the origin of liturgies [Hammond].

Matthew Henry's Concise Commentary

1:17-23 Sensual men separate from Christ, and his church, and join themselves to the devil, the world, and the flesh, by ungodly and sinful practices. That is infinitely worse than to separate from any branch of the visible church on account of opinions, or modes and circumstances of outward government or worship. Sensual men have not the spirit of holiness, which whoever has not, does not belong to Christ. The grace of faith is most holy, as it works by love, purifies the heart, and overcomes the world, by which it is distinguished from a false and dead faith. Our prayers are most likely to prevail, when we pray in the Holy Ghost, under his guidance and influence, according to the rule of his word, with faith, fervency, and earnestness; this is praying in the Holy Ghost. And a believing expectation of eternal life will arm us against the snares of sin: lively faith in this blessed hope will help us to mortify our lusts. We must watch over one another; faithfully, yet prudently reprove each other, and set a good example to all about us. This must be done with compassion, making a difference between the weak and the wilful. Some we must treat with tenderness. Others save with fear; urging the terrors of the Lord. All endeavours must be joined with decided abhorrence of crimes, and care be taken to avoid whatever led to, or was connected with fellowship with them, in works of darkness, keeping far from what is, or appears to be evil.