The primary reason to be able to both speak in a tongue and prophesy was to edify the Church. The secondary value was to be able to go out and publicly expound to those who were in unbelief. Paul was trying to get the brethren in the class not to war against each other, not to be factional, not to show off with their gifts, and not to boast of which leader they followed. In other words, his main purpose was to unify the brethren and to create a good atmosphere for Christian development and growth of the fruitage of the Spirit, let alone for the benefits that would accrue to others through such a ministry.
Paul did not criticize the possession of tongues in his day. In fact, he said, “I would to God that all had this personal, private experience in understanding,” but he wanted the brethren to go further and interpret and be a blessing to others. “Greater is he that prophesieth” was his thought. Evidently, unknown tongues were the most common mechanical gift back there, but they were also a lower gift. However, if one could interpret as well as speak in an unknown tongue, that was a higher step, more or less equivalent to prophecy.
Why did Paul say, “I would that ye all spake with tongues”? If all of the Corinthians spoke in tongues, they would not be examining one another with such statements as “I can speak in tongues, but you cannot.” The Corinthians might even have prayed that their wife or friend would get this gift, but receiving a gift was God’s doing. Paul hoped they could all speak in tongues so that envy and jealousy would not be prevalent in their midst. When an individual consecrated, he got one of the gifts but not necessarily the gift of tongues. However, the brethren misunderstood because more people got tongues than any of the other gifts.