Question:
Jude 20. What is praying in the Holy Spirit? Is this the same as tongues? How does this build you up?

Answer:
Jude 20 says: “But ye, beloved, building up yourselves on your most holy faith, praying in the Holy Ghost,”

The Lord’s words in John 15:4, 7 suggest that our praying should flow from our communion with Him. “Abide in Me, and I in you. As the branch cannot bear fruit of itself, except it abide in the vine; no more can ye, except ye abide in me. . . . If ye abide in Me, and My words abide in you, ye shall ask what ye will, and it shall be done unto you.”
If we are close to Christ by being occupied with Him, the Spirit will communicate to us people and things to pray for. If a person’s name pops in my head, maybe the Holy Spirit is telling me to pray for them.
How does this build up? It builds us up collectively as we pray for one another, and it may lead us to not just pray but also to do something about it. At the end of Jude 20 is a comma, so this is not the end of the exhortation. Verse 21 goes on to say: “Keep yourselves in the love of God.” Do I really realize that He loves me? “Looking for the mercy of our Lord….” Do I really live my life as though He could come at any moment? Live (1) in His love, (2) looking for His return.
To pray in the Holy Spirit, we must “be filled with the Spirit” (Ephesians 5:18). Being filled with the Spirit is not how much of the Spirit I have [“For . . . God giveth not the Spirit by measure” (John 3:34). We either have the Spirit or we don’t.] But how much I let Him control me! So when I pray in the Holy Spirit it is praying for the things that He would have me pray for; not selfish things or things not good for me, but the Spirit knows (even if we don’t) how to pray for a situation and talks to the Father for us according to God’s will (Romans 8:26).