“In him you also, when you heard the word of truth, the gospel of your salvation, and believed in him, were sealed with the promised Holy Spirit…” Ephesians 1:13 (ESV)
(an extended paraphrase) “When you believed God’s truthful message, the gospel that saved you, you were placed into Christ and stamped with a seal that cannot be broken, erased, deleted or tampered with. This unbreakable seal is the Holy Spirit Himself and signifies God’s total approval of you! When He looked over all that He had done in you, He saw nothing flawed or inferior whatsoever, but all was as it should be. That seal tells everyone that you belong to God and no one can ever interfere with the package! Even more, this Holy Spirit-stamp means the postage is pre-paid to get you all the way to your ultimate destination! So you can be sure that once your journey with the Lord began, you will make it all the way to the final destination – safe forever, home at last.”