“[Having] believed, ye were sealed with that Holy Spirit of promise” (Eph. 1:13).
Of all the wonderful Scripture passages on the eternal security of the believer in Christ, this is perhaps the most blessed of all.
“[Having] heard the Word of truth you believed,” says the Apostle, and “[having] believed, you were sealed.” Now a seal speaks of finality and permanency, whether it be the official seal on an important document, the seal on an electric transformer or the seal on a jar of preserves. But the most blessed fact of all is that the believer in Christ is “sealed with that Holy Spirit of promise.” Mark well, he is sealed not by the Spirit but with the Spirit; the Spirit Himself is the seal.
Here, let us say, is a woman sealing jars of preserves with wax. The jars are sealed by the woman, but with the wax. Thus the humblest believer is sealed with the Spirit. It is He Himself who keeps us safe in Christ through all eternity.
And this is but the “earnest,” the first installment, “of our inheritance” (Eph. 1:14), for the Spirit keeps us secure in “this present evil age” so that “in the ages to come” God might show “the exceeding riches of His grace in His kindness toward us through Christ Jesus” (Eph. 2:7).
Little wonder the Apostle closes this passage on our security with those appropriate words: “To the praise of His glory” (Eph. 1:14).
What some theologians have called “the perseverance of saints” is not our perseverance at all, but God’s faithfulness. We have not persevered; He has preserved us by His grace for His glory. source