After writing for some time on this topic, I have found out that there is an issue which I have overlooked, and therefore let us turn back to it before answering the "million dollar question".
When defining the Gift of Tongues, there seems to be the argument that tongues could also refer to a private prayer tongue — a tongue for the expression of intimacy between the believer and God, and therefore different from the other "public tongues"; a second class of 'tongues'. Related to that of course is that the purpose of such tongues are for self-edification, and thus do not function as biblical signs like the other tongues mentioned in ie Acts 2.
The primary proof-text for this is 1 Cor. 14: 2-4, which is as follows:
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. On the other hand, the one who prophesies speaks to people for their upbuilding and encouragement and consolation. The one who speaks in a tongue builds up himself, but the one who prophesies builds up the church. (1 Cor. 14:2-4)
Certainly, a surface level reading seems to suggest what the Charismatics are saying; that there are tongues which are private prayer languages meant for self-edification. Another such proof-text for the private prayer language is Rom. 8:26-27:
Likewise the Spirit helps us in our weakness. For we do not know what to pray for as we ought, but the Spirit himself intercedes for us with groanings too deep for words. And he who searches hearts knows what is the mind of the Spirit, because the Spirit intercedes for the saints according to the will of God. (Rom. 8:26-27)
However, is that what those two verses actually teach, or is this just another case of eisegesis; reading one's own interpretation into the text?
Let us start by looking at 1 Cor. 14:2-4, and this time let us interpret the verses in light of their context.
The arena upon which 1 Cor. 14 plays out is in the Church, or more specifically the Body Life of the Church; to edify the Church. Paul is here exhorting the Corinthians to focus on the Gift of Prophecy rather than to focus on their boasting in Tongues, which they are abusing. Paul therefore utilizes the language of contrasts here, contrasting the Gift of Prophecy with the Gift of Tongues in their usefulness in the life of a Church.
It is in this context that we come to verse 2 of 1 Cor. 14. Verse 2 and 3 form a pair of contrasts, and therefore inform us as to what Paul was getting at in verse 2. As it can be seen, verse 3 mentions the utility of the Gift of Prophecy in upbuilding, encouragement and consolation within the Church of Christ. Verse 2 therefore speaks similarly about the utility of the Gift of Tongues within the Body Life of the Church of God. Thus, when it is stated that the 'one who speaks not to men but to God', this is contrasted with the fact that Prophecy speaks to Man. The phrase 'No one understands him' is contrasted with the fact that all would understand prophecy (we will get to prophecy later), and 'utters mysteries' is contrasted with Prophecy uttering clear and coherent words. Similarly, a pair of contrast exists between verse 4a and verse 4b, with Tongues said to edify oneself contrasted with Prophecy edifying the Church. From all this therefore, 1 Cor. 14:2-4 can be seen to be not promoting a private prayer language after all, but is actually stating that the Gift of Tongues in the Body Life of the Church only edifies the speaker. This is because in general during normal Sunday services, no one except God can understand what they are saying and therefore they are uttering mysteries by the power of the Holy Spirit. Barring the situation which truly warrents it, ie when a person possibly a foreigner who knows the likely obscure language comes thus giving the Tongue-speaker a chance for their tongues to be ueful as a sign, speaking in Tongues during services will only edify oneself and not others.
1 Cor. 14:2-4 has therefore be shown within its proper context to be not promoting or describing a private prayer language after all, but rather the non-utility of Tongues in the Church's Life. So what about Rom. 8:26-27?
Rom. 8:26-27 is talking about the topic of prayer, or rather how the Spirit helps us when we find it difficult to pray. All of us have our points and times of weaknesses, and even when we are stronger does not mean we are actually strong. So in our times of weakness, God has promised to help us by the 'Spirit Himself interceding for us with groanings too deep for words'. Verse 27 is the rationale describing why the Spirit can so help us, where it is stated that he (Jesus cf Jer. 17:10; Rev. 2:23) who searches the heart know the mind of the Spirit and the reason for that is that 'the Spirit intercedes for the saints according to the will of God'. But what does this all mean?
We must always remember that the topic here is on prayer, and how God can help us in prayer despite our weaknesses. In verse 27, the Holy Spirit is said to intercede for the saints according to the will of God, and because the Holy Spirit does that, Jesus who searches the heart knows the mind of the Spirit. The mind of the Spirit refers to the intercession of the saints according to the will of God, so when Jesus searches the heart of the believer who prays, he sees His own will on the matter there. But how can this be unless the Spirit puts the will of God on the matter onto our hearts, since Jesus is here searching the heart of believers, not the heart of the Holy Spirit? Verse 27 therefore states that Jesus who searches the heart of believers will find there the exact will of God, the mind of the Spirit, which is placed there by the Holy Spirit. Together with verse 26, the Spirit is therefore stated as interceding for us by showing us the will of God for that matter so that we will pray God's will.
This of course leaves the phrase "groanings too deep for words", which doesn't seem to fit in. This could however be describing our experience in travailing in prayer, for such describes the emotional state of those who have wept and pleaded for God mightily in prayer, who do not know how to pray as they ought to and therefore seek God to help them even though they do not know how to ask God for aid. This therefore shows also that praying according to the will of God, which is promised here in this passage of two verses, can only be done through serious seeking after God and much hardship even. Do we wonder why sometimes it seems as if prayer is so dry and that nothing happens? Is it because we are not travailing mightily in prayer with groanings too deep for words? (This is a rebuke for me also btw).
As it can be seen, both 1 Cor. 14:2-4 and Rom. 8:26-27 do not in fact support the position of a class of tongues being private prayer languages, when interpreted correctly within its contexts. There is therefore only one type of tongue in the whole of Scripture — the biblical Gift of Tongues, and it is only of known human languages and does not function as a private prayer language.
[to be continued]