Ephesians 6:18 says, “Praying always with all prayer and supplication in the spirit…” Jude 20 says, “…building up yourselves on your most holy faith, praying in the Holy Ghost.”
Notice the similarity of these two phrases, “praying in the Spirit” and “praying in the Holy Ghost.” In 1 Corinthians 14, Paul uses similar language when he describes speaking or praying in other tongues. In verse 2 he refers to speaking in other tongues as speaking in the spirit: For he that speaketh in an unknown tongue speaketh not unto men, but unto God: for no man understandeth him; howbeit in the spirit he speaketh mysteries.”
Jude 20 says we are to build up ourselves on our most holy faith by praying in the Holy Ghost. Paul uses similar language in 1 Corinthians 14:4 where he says, “He that speaketh in an unknown tongue edifieth himself…” To edify is to build up.
Now notice 1 Corinthians 14:14-15, “For if I pray in an unknown tongue, my spirit prayeth, but my understanding is unfruitful. What is it then? I will pray with the spirit, and I will pray with the understanding also: I will sing with the spirit, and I will sing with the understanding also.
In 1 Corinthians 14, Paul describes praying in other tongues as “praying with, or in, the Spirit” and he uses this language in contrast to praying with the understanding. He also refers to singing in the Spirit in contrast to singing with the understanding.
Paul’s refers to other tongues as (1) speaking in the Spirit, (2) praying with the Spirit, and (3) singing with the Spirit.