Paul said the basis for edification is knowing what is said. He said tongue speakers edified themselves. That is, they knew what they were saying along with those hearing their interpretation. This proves how false today's "tongues" are.
Discernment is needed when applying Paul's words in the context of the message he is giving about tongues as spiritual gift.
1 Corinthians 14:1Follow after charity, and desire spiritual gifts, but rather that ye may prophesy.
Therein s the topic; Paul is starting the topic that if any believer seeks a spiritual gift, they were to seek the gift of prophesy over all spiritual gifts. He goes on to explain why by comparing the gift of tongues against the gift of prophesy fro why prophesy is better because tongues is not a stand alone gift.
2 For he that speaketh in an unknown tongue speaketh not unto men, but unto God: for no man understandeth him; howbeit in the spirit he speaketh mysteries. 3 But he that prophesieth speaketh unto men to edification, and exhortation, and comfort.
When you add verses 2:3 together, it is the same point Paul is trying to make in verse 4 but still a mystery as verse 2.
4 He that speaketh in an unknown tongue edifieth himself; but he that prophesieth edifieth the church.
Paul explains why prophesy is better because tongues has to be interpreted thus not a stand alone gift.
5 I would that ye all spake with tongues but rather that ye prophesied:
for greater is he that prophesieth than he that speaketh with tongues, except he interpret, that the church may receive edifying.
In the context of the message as we read on, the tongue speaker cannot know what they are saying for why they are to pray that another interpret. That is why it is unfruitful to the tongue speaker because he is praying to for interpretation to understand it & not just from hearing that tongue from another tongue speaker.
11 Therefore if I know not the meaning of the voice, I shall be unto him that speaketh a barbarian, and he that speaketh shall be a barbarian unto me. 12 Even so ye, forasmuch as ye are zealous of spiritual gifts, seek that ye may excel to the edifying of the church.
13 Wherefore let him that speaketh in an unknown tongue pray that he may interpret. 14 For if I pray in an unknown tongue, my spirit prayeth, but my understanding is unfruitful. 15 What is it then? I will pray with the spirit, and I will pray with the understanding also: I will sing with the spirit, and I will sing with the understanding also.
Since chapter 12 came before chapter 14, we are to understand how Paul is seaking and what he had meant in the precedent he has set from before.
1 Corinthians 12:4 Now there are diversities of gifts, but the same Spirit. 5 And there are differences of administrations, but the same Lord. 6 And there are diversities of operations, but it is the same God which worketh all in all.
7 But the manifestation of the Spirit is given to every man to profit withal. 8 For to one is given by the Spirit the word of wisdom;
to another the word of knowledge by the same Spirit; 9
To another faith by the same Spirit;
to another the gifts of healing by the same Spirit; 10
To another the working of miracles
; to another prophecy;
to another discerning of spirits;
to another divers kinds of tongues; to another the interpretation of tongues: 11 But all these worketh that one and the selfsame Spirit,
dividing to every man severally as he will. 12 For as the body is one, and hath many members, and all the members of that one body, being many, are one body: so also is Christ.
That means no one member can speak in tongues & interpret that tongue; when only another can do it. Confirmation as to how that it so in the body when believers thinks they can speak in tongues & interpret that tongue at the same time is here.
14 For the body is not one member, but many.....19 And if they were all one member, where were the body? 20 But now are they many members, yet but one body.
21 And the eye cannot say unto the hand, I have no need of thee: nor again the head to the feet, I have no need of you.
Look at how they are to prophesy...
1 Corinthians 14:29 Let the prophets speak two or three,
and let the other judge.
Now look at how they are to speak in tongues;
1 Corinthians 14:27 If any man speak in an unknown tongue, let it be by two, or at the most by three, and that by course;
and let one interpret.
When reading the letter in context, the one judging cannot be of the 2 or 3 prophesying any more than the one interpreting cannot be of the 2 or 3 speaking in tongues.
In closing in regards to verse 2... on how they are not speaking TO God but God understands what is being said.. we read..
28 But if there be no interpreter, let him keep silence in the church; and let him speak to himself, and to God.
Is the man crazy in speaking to himself and to God? No. He understands what he is saying as God does for why he is not speaking TO God in verse 2 either. When you have 2 or 3 speaking in tongues, and a visitor in church speaks out of turn, he is commanded to be silent. This is rightly dividing the word of truth because if he was speaking as the Holy Spirit manifested, that would be like we can tell the Holy Spirit to be silent or shut up? No. So it is not the Holy Spirit speaking but someone is speaking out of turn as a visiting foreigner and proof of that is there is no interpretation for what that man is saying. Hence tongues is not a stand alone gift for why he is commanded to be silent.
I can only hope in the Lod that He will help you understand the way Paul is writing but in the whole context of what he is sharing in that letter about the use of God's gift of tongues in the church for why we should seek prophesy over all gifts..