The law of first mention may be said to be the principle that requires one to go to that portion of the Scriptures where a doctrine is mentioned for the first time and to study the first occurrence of the same in order to get the fundamental inherent meaning of that doctrine. When we thus see the first appearance, which is usually in the simplest form, we can then examine the doctrine in other portions of the Word that were given later. We shall see that the fundamental concept in the first occurrence remains dominant as a rule, and colors all later additions to that doctrine. In view of this fact, it becomes imperative that we understand the law of first mention.
An Apostolic example of this law would be the infilling of the Holy Ghost with the evidence of speaking in other tongues. In Acts 2, the Holy Ghost is poured out upon believers on the Day of Pentecost. This experience was initiated as the Spirit’s outpouring, and was evidenced by those being filled speaking with other tongues as the Spirit gave them utterance. Further examples in the New Testament reveal that those being filled with the Holy Ghost continued to exhibit the same evidence. Thus, the law of first mention proves out the fact that scripture declares tongues to be the evidence of one being filled with the Spirit.