in His new Temple. He does not enter because we are especially virtuous, or successful. He enters because we have been bought by the Father through the costly sacrifice of His Son, and belong to Him for ever as His own Family. We may only be babes of an hour old, but we are Sons nevertheless, and The Holy Spirit witnesses to this overwhelming fact without delay (Acts 10:44-47). It is, as it were, God's Heavenly acknowledgment that a Son has been born (Rom. 8:16; Gal. 4:6; Acts 2:38; Eph. 2:22).
This ability to speak in one unknown tongue is then the initial sign that The Holy Ghost is now in His Temple: but it is only the initial sign, and is meant to be followed by other gifts of more practical importance. The first of these to be considered is "kinds of tongues", i.e. the ability to speak in more than one new language. The initial sign of the Baptism is not "speaking in tongues", but "speaking in a tongue". "Speaking in tongues" i.e. more than one tongue, is one of the nine Gifts of The Spirit.
The value of speaking in one tongue is that we speak words, which we do not ourselves understand, to God, and so edify ourselves by pouring out our heart to Him in praise. So far however as our neighbour is concerned it will only mystify him, and he will say we are mad or drunk, and not be edified (1 Cor 14:23) unless he may happen to understand the language we are speaking, in which case of course he will be forced to think, and ask what it is and what it means, as happened on the day of Pentecost (Acts 2:7-13).