This is an amazing promise. The word for "secret" means the "inner counsel," evidently of the triune God Himself.
But how can those who fear the Lord really know the secret counsels of the Godhead? The answer can only be by divine revelation to God’s prophets. Thus the prophet Amos affirms: "Surely the Lord GOD will do nothing, but [unless] he revealeth his secret unto his servants the prophets" (Amos 3:7).
When these ancient promises were given, however, much of God’s revelation, though already "settled in heaven" (Psalm 119:89), was still not revealed to men. Then Christ came and promised His disciples, "The Comforter, which is the Holy Ghost . . . shall teach you all things" (John 14:26).
"God, who at sundry times and in divers manners spake in time past unto the fathers by the prophets, Hath in these last days spoken unto us by his Son" (Hebrews 1:1-2). In addition to the twelve disciples, God then also called the apostle Paul, and through these men, the Son would convey to those who fear Him all the rest of His revelation. "By revelation he made known unto me the mystery; (. . . Whereby, when ye read, ye may understand my knowledge in the mystery of Christ) Which in other ages was not made known unto the sons of men, as it is now revealed unto his holy apostles and prophets by the Spirit" (Ephesians 3:3-5).
Finally, "the secret of the Lord" was completed in written form by John, the last of the apostles, with nothing else to be either added or deleted (Revelation 22:18-19), that "the mystery of God should be finished, as he hath declared to his servants the prophets" (Revelation 10:7). All we shall ever need to know of God’s eternal counsels is now available to all who desire to know, in the Holy Scriptures. HMM http://www.icr.org/article/6073/