1 Corinthians 14:13-19

Therefore let one who speaks in a tongue pray that he may [be gifted to] translate or explain [what he says]. For if I pray in a tongue, my spirit prays, but my mind is unproductive [because it does not understand what my spirit is praying]. Then what am I to do? I will pray with the spirit [by the Holy Spirit that is within me] and I will pray with the mind [using words I understand]; I will sing with the spirit [by the Holy Spirit that is within me] and I will sing with the mind [using words I understand]. Otherwise if you bless [and give thanks to God] in the spirit only, how will any outsider or someone who is not gifted [in spiritual matters] say the “Amen” [of agreement] to your thanksgiving, since he does not know what you are saying? [1 Chr 16:36; Ps 106:48] You are giving thanks well enough [in a way that God is glorified], but the other person [who does not understand you] is not edified [and spiritually strengthened since he cannot join in your thanksgiving]. I thank God that I speak in [unknown] tongues more than all of you; nevertheless, in public worship I would rather say five understandable words in order to instruct others, than ten thousand words in a tongue [which others cannot understand].