1 Corinthians 2:13

also--We not only know by the Holy Ghost, but we also speak the "things freely given to us of God" (Co1 2:12). which the Holy Ghost teacheth--The old manuscripts read "the Spirit" simply, without "Holy." comparing spiritual things with spiritual--expounding the Spirit-inspired Old Testament Scripture, by comparison with the Gospel which Jesus by the same Spirit revealed [GROTIUS]; and conversely illustrating the Gospel mysteries by comparing them with the Old Testament types [CHRYSOSTOM]. So the Greek word is translated, "comparing" (Co2 10:12). WAHL (Key of the New Testament) translates, "explaining (as the Greek is translated, Gen 40:8, the Septuagint) to spiritual (that is, Spirit-taught) men, spiritual things (the things which we ourselves are taught by the Spirit)." Spirit-taught men alone can comprehend spiritual truths. This accords with Co1 2:6, Co1 2:9-10, Co1 2:14-15; Co1 3:1. ALFORD translates, "Putting together (combining) spirituals with spirituals"; that is, attaching spiritual words to spiritual things, which we should not do, if we were to use words of worldly wisdom to expound spiritual things (so Co1 2:1, Co1 2:4; Pe1 4:11). Perhaps the generality of the neuters is designed to comprehend these several notions by implication.

— Jamieson-Fausset-Brown Commentary (public domain)