Them in let each of them keep silence refers to the people speaking in tongues in verse 27. This is why Good News Bible adds the words “the one who speaks in strange tongues must be quiet.” Translators will do well to follow Good News Bible‘s example.

Barrett points out that the word to in the phrases translated to himself and to God probably varies in meaning. The first phrase is better translated in many languages as “for himself,” that is, silently and inwardly, and the second one “to God.”

Quoted with permission from Ellingworth, Paul and Hatton, Howard A. A Handbook on Paul’s First Letter to the Corinthians, 2nd edition. (UBS Handbook Series). New York: UBS, 1985/1994. For this and other handbooks for translators see here .