I Corinthians 11:19 states that heresies serve to sever those who are not approved of God from those who are approved. The division within the Church over tongues is God ordained because of its function as a sign -- to confirm true brethren and condemn false brethren. Thus, the issue of tongues is not some minor squabble Christians should overlook as some would have us think.
Jesus listed speaking in tongues as a divine sign of confirmation which would follow (be endemic to) the collective body of Christ (Mark 16:17-18). However, many today who say they belong to Jesus not only don't accept tongues as a "sign following believers," they actually go so far as to say that Jesus' words in Mark 16:16-18 shouldn't even be in the Bible!
How can people claim to be following Jesus when they don't accept the things which He has said and won't believe the signs He has sent? An understanding of I Corinthians 14:21-22 gives a profound answer to this question!
"In the law it is written, With [or through] men of other tongues and other lips will I [God] speak to this people [God's people]; and yet for all that will they not hear me, saith the Lord" (I Cor. 14:21). Verse 21 quotes Isaiah 28:11-12 which says: "For with stammering lips and another tongue will he [the Lord] speak to this people [God's people]. To whom he said, This is the rest [in the Holy Ghost] wherewith ye may cause the weary to rest; and this [rest in the Holy Ghost] is the refreshing [mentioned in Acts 3:19 & 2:38]: YET they [the stiffnecked among God's people] would not hear [not accept this as God's doing]."
Now the next verse, I Cor. 14:22. "Wherefore [because they rejected tongues], tongues are for a sign, not to them that believe [accept tongues as from God], but to [AGAINST] them that believe not [won't accept]: but prophesying [preaching] serveth not [does no good] for them that believe not [who won't accept because they have closed their hearts], but [serves] for them which believe [have open hearts to all God has]."
Do you see what these verses are saying? A paraphrase of I Cor. 14:21-25 could read as follows. "Isaiah wrote that one day God would, by His Spirit, speak through men in an unknown tongue to those who were supposed to be His own people. Yet, many would reject this phenomenon as a sign of God's promised rest in His Holy Spirit.
"Wherefore, the accepting or rejecting of tongues is a sign. Those who say they are God's people and accept tongues as being of God show that they have a heart to 'believe' in all God has. Those who say they are God's people but reject tongues as being of God show that they have a heart that actually 'believes not.' So even regular preaching will not benefit those who 'believe not' within the local church, because they are closed to anything that goes against their preconceived ideas. But preaching edifies those who have an open heart to 'believe' among the brethren, because they have hearts open to God's truth. So this is how tongues serve as a sign.
"Now let's look at how tongues should be used in a local church service. If everyone only speaks in tongues and some 'unbelievers,' heathens, come in who are 'unlearned' about the gifts of God, they will think you are crazy.
"But if everyone strives to preach at the church gathering and one who 'believes not' in Christ, or is unlearned of the things of God, comes in, he will be convinced and judged of all his sins.
"This individual will fall on his face and get saved because all the secrets of his heart have been manifest. He will worship God and say that God is in you all for certain."
The above is the accurate meaning of I Cor. 14:21-25. I'll also say that this understanding of this scripture can only be gained from reading the passage in the KJV with the anointing of the Holy Ghost.
Modern translations penned by theologically and denominationally biased minds have totally missed what this is saying and actually render the passage to read in such a way as to make it contradict itself -- by saying tongues are for unbelievers in 22 and not for them in 23, and by saying that preaching is not for unbelievers in 22 but for them in 24!
The whole understanding stems from identifying "this people" in verse 21. Once this is done it is evident that the "believe nots" of 22 are false brethren closed to truth, while the "believe nots" of 24 are sinners who are open to God! The "believers" of 22 are true saints or seekers but the "believe nots" of 22 is a false Christian who will not believe!
Tongues are for a sign! This sign will follow the true people of God collectively and will be accepted by them as from God (Mk. 16:17). It will be a sign against those "among us" who reject tongues as from God saying it is not for today and even of the devil (I Cor. 14:21-22).
"Brethren, covet to prophesy, and forbid not to speak with tongues. Let all things be done decently and in order" (I Cor. 14:39-40).
"If any man think himself to be a prophet, or spiritual, let him acknowledge that the things that I write unto you are the commandments of the Lord. But if any man be ignorant, let him be ignorant" (I Cor. 14:37-38).