The need of interpreting Scripture by Scripture
The general principle is expressed in the well-known words “comparing spiritual things with spiritual” (1 Cor. 2:13), for while the preceding clause has reference more especially to the Divine inspiration by which the apostle taught, as the authoritative mouthpiece of the Lord, yet both verses 12 and 14 treat of the understanding of spiritual things, and therefore we consider that the last clause of verse 13 has a double force. …Charles Hodge paraphrases “comparing spiritual things with spiritual” by “explaining the things of the Spirit in the words of the Spirit,” pointing out that the word “spiritual” has no substantive connected with it, and thus most naturally agrees with “words” in the former sentence.
To a very large extent, and far more so than any uninspired book, the Bible is a self-explaining volume: not only because it records the performance of its promises and the fulfillment of its prophecies, not only because its types and antitypes mutually unfold each other, but because all its fundamental truths may be discovered by means of its own contents, without reference to anything ab extra or outside itself. When difficulty be experienced in one passage it may be resolved by a comparison and examination of other passages, where the same or similar words occur, or where the same or similar subjects are dealt with at greater length or explained more clearly.
The principal subjects treated in the Scriptures are presented to us more or less piecemeal, being scattered over its pages and made known under various aspects, some clearly and fully, others more remotely and tersely: in different connections and with different accompaniments in the several passages where they occur. This was designed by God in His manifold wisdom to make us search His Word. It is evident that if we are to apprehend His fully made known mind on any particular subject we must collect and collate all passages in which it is adverted to, or in which a similar thought or sentiment is expressed; and by this method we may be assured that if we conduct our investigation in a right spirit, and with diligence and perseverance, we shall arrive at a clear knowledge of His revealed will.