"The LORD shall reign for ever and ever" (Exodus 15:18).
The Bible is a book of eternity; its words "For ever . . . settled in heaven" (Psalm 119:89). The theme of eternity is prominent throughout; in fact, the words "for ever," "everlasting," and the like occur more than 600 times. Many such occurrences (49 to be exact, or 7 x 7) seem to make the concept even more complete, being combined either as "for ever and ever" or "from everlasting to everlasting."
The first of these is in our text: "The LORD shall reign for ever and ever." He is the eternal King of all creation! How beautiful and appropriate it is, then, to find that the last (the 49th) of these occurrences tells us that we--His redeemed saints--also "shall reign for ever and ever" (Revelation 22:5).
To note just a few of the other truths that will last for ever and ever, consider first of all, the creation: "Praise ye Him, sun and moon: praise Him, all ye stars of light. . . . For He commanded, and they were created. He hath also stablished them for ever and ever: He hath made a decree which shall not pass" (Psalm 148:3,5-6). Not only the world of God, but also the Word of God, shall endure eternally. "All His commandments are sure. They stand fast for ever and ever, and are done in truth and uprightness. . . . So shall I keep thy law continually for ever and ever" (Psalm 111:7-8; 119:44).
On the other hand, those who reject God and His Word will endure forever, but will be forgotten forever. "Thou hast destroyed the wicked, thou hast put out their name for ever and ever" (Psalm 9:5). "And the smoke of their torment ascendeth up for ever and ever" (Revelation 14:11).
"But the mercy of the LORD is from everlasting to everlasting upon them that fear Him" (Psalm 103:17). "And they that be wise shall shine as the brightness of the firmament; and they that turn many to righteousness as the stars for ever and ever" (Daniel 12:3). HMM