After all Jude has said in the preceding verses about watching out for the ungodly and how the ungodly behave, now he says, "but ye beloved…"  So in contrast to and because of the world’s attitude and behavior he tells us what we are to do.

We are to build up our most holy faith, praying in the Holy Ghost.  Praying in the Spirit, or praying as the Holy Spirit gives the words, including in other tongues (as described in Acts 2, Acts 10:44-46, Acts 19:1-6, Romans 8:26-27, and 1 Corinthians 14:15), builds up our faith.

One of the purposes and advantages of praying in tongues is to build ourselves up in faith.  There is a personal spiritual advantage to us praying in tongues.  Not only are we praying according to the will of God (Romans 8:27) which may be unknown to our natural mind, but we are building up our faith as well.

Jesus told His disciples not to leave Jerusalem until they were filled with the Spirit.  In other words, don’t go out and try to do what He’s called you to do without the infilling of His Spirit.  We need the power, anointing, guidance, comfort and language of the Holy Spirit in order to effectively do what God has called us to do.

Confession:

I will build up my most holy faith by praying in the Holy Ghost.