Paul’s statement that the person who speaks in tongues speaks to God
corresponds to the account of Cornelius and his household’s speaking in tongues and extolling God
(Acts 10:46).
Yet a person who speaks in (uninterpreted) tongues speaks only to God, since his words are incomprehensible to everyone but God. This is why prophesy, which is comprehensible to everyone, should be desired more than tongues (1 Corinthians 14:1).
As there are no capital letters in biblical Greek, it is difficult to say with certainty whether the word for spirit
in this verse refers to a man’s spirit or to the Holy Spirit. In 1 Corinthians 14:14–15 the word probably refers to a man’s spirit. Here, however, the word mysteries
suggests that Paul has the Holy Spirit in view (see 1 Corinthians 13:2 and its comments).
2 For one who speaks in a tongue speaks not to men but to God; for no one understands him, but he utters mysteries in the Spirit.