Regarding the passages in 1 Corinthians 14, it does seem contradictory that under some conditions it’s improper to use tongues with an unbeliever even though they’re for them. And even more, that at times it’s better to use prophecy than tongues with an unbeliever, even though prophecy is not for them, while tongues is. And just to top it off, it actually appears as if God is saying the gift of tongues (which He designed as a sign to unbelievers) will always be ineffective with them.
1 Corinthians 14:21b "and yet, for all that, they will not hear Me," says the Lord. (NKJV)
So what would be the point then? Why would anyone ever speak in tongues if the goal of speech is effective communication? And how can ineffective speech be consider a spiritual gift when without it, God promises (Isaiah 55:11) His word will not return void?
To solve this paradox, one needs to distinguish between the “sign” of tongues, and what was said while speaking in them. We all know what signs are, for they are everywhere in life. Signs are objects containing typically short and to the point messages directed at select people groups. Some communicate with words, some with symbols, and others with a variety tools. To understand the sign portion of tongues, we must ask ourselves “Why did God invent this gift?” And also ”What was He trying to communicate by bestowing this gift on the believers He did at the times He did? When we grasp the answers to these questions (when we know what the sign of tongues said) we will see there are no contradictions within the passages under question.
I see four distinct situations in Scripture where God used tongues to convey a message. In the first, He tells us its purpose was to confirm the words of the Apostles, to give credibility to the New Testament truths they were proclaiming (Mark 16:14-20, 2 Corinthians 12:12). This particular use of tongues as a sign to the observers would have read “These Words Are True.”
The second use of tongues would be when God acknowledged the Gentile converts in Cornelius’s household (Acts 10:1-11:18, 15:6-11). Here, Peter had a vision, and while wondering about its meaning, God began explaining it to him by sending men to his gate seeking an audience with him. Per their request and God’s instructions, Peter went with them and shared the gospel. Upon hearing and embracing it, the new Gentile believers were gifted with tongues. By this, Peter came to understand the meaning of the vision, that God was telling him salvation was for people of all languages (Acts 10:28b), and that it came in the same way to all (Acts 10:34-35, 43), that being through faith in the Lord Jesus Christ (Acts 11:17, 15:7b). This particular use of tongues as a sign to Peter would have read “Salvation Comes Through Faith In Jesus, And Is For People Of All Languages.”
The third use of tongues would be when God confirmed that John’s disciples were His people too (Acts 19:1-7). They were genuine Old Testament believers who had not yet been introduced to New Testament truths. This particular use of tongues as a sign would have been a continuation of the second, and would have read “Including Old Testament Believers.”
And the fourth use of tongues would have been at Pentecost itself (Acts 2:1-13). If I had been an observer and took the time to consider what God was saying by gifting those people with tongues, I would have concluded that He must have wanted the Gentiles to hear His truths really bad. And also, I would have wondered why He was speaking through the individuals He was, rather than through mainstream Israel. Paul confirms and explains this in Romans chapters 9-11 where he tells us that because of Israel’s extreme unfaithfulness to God (Romans 10:21), that He was turning to the Gentiles with the gospel message (Romans 11:11). If Israel was going to provoke Him to jealousy by giving their love to His enemies (Deuteronomy 32:16-22), then He was going to provoke them to jealousy by giving His love to their enemies (Romans 10:19). And also, in quoting out of Isaiah, Paul declares the reason why God was working through those He did, rather than through the leadership in Israel.
1 Corinthians 14:21 In the law it is written: "With men of other tongues and other lips I will speak to this people; and yet, for all that, they will not hear Me," says the Lord. (NKJV)
Isaiah 28:11a For with stammering lips and another tongue he will speak to this people... 12b yet they would not hear. (NKJV)
This quote was itself a quote from the list of promised blessings for obedience and curses for disobedience in Deuteronomy 28 that God gave Israel before entering the Promised Land. The promise Paul associated with tongues is the curse found in verse 49. This curse was quoted by the prophets (Isaiah 28:7-19, Jeremiah 5:14-19, Ezekiel 3:1-11, Isaiah 32:1-4, and Isaiah 33) to warn Israel of impending judgment. God had told them that if they were unfaithful to Him, if they didn’t serve Him with joy and gladness of heart, but rather gave their love to the gods of the Gentiles (Deuteronomy 28:14-15, 45-49), that He would make them serve the Gentiles. If they wanted to worship His enemies, then he would make them serve their enemies. He would fulfill this threat by raising up a foreign military power (men of another tongue) to wage war against them, taking them prisoners. From this we conclude that the tongues of Pentecost were a sign to unbelieving Israel (who should have known their meaning from the Old Testament) that God was judging them. Their warning from Jesus (Matthew 21:43) was now coming to pass in that God was stripping them of their role in His kingdom by forming the Church as their replacement. Therefore this particular use of tongues as a sign to unbelieving Israel would have read “Your Sins Are Great, So Repent And Place Your Faith In Jesus, Or Face Judgment.”
I believe with this understanding the passages in 1 Corinthians 14 should be clear, containing no contradictions. As a sign, God used tongues to say “These Words Are True. Salvation Comes Through Faith In Jesus, And Is For People Of All Languages, Including Old Testament Believers. Your Sins Are Great, So Repent And Place Your Faith In Jesus, Or Face Judgment.” When used as a form of verbal communication to unbelievers (rather than as a sign), Paul is simply saying that tongues should only be spoken when understood, and in an orderly manner, as the purpose of speech is effective two way communication. In conjunction with this, he also says that if this can’t be done, that prophecy (even though its primary purpose is not for unbelievers) is a more effective form of communication with them, than tongues which are not understood. For words are words, whether they come easily, or through much study.
See http://www.tonguesbook.com for an in-depth look at this.