“But you are not controlled by your sinful nature. You are controlled by the Spirit if you have the Spirit of God living in you. (And remember that those who do not have the Spirit of Christ living in them do not belong to him at all.)” (Romans 8:9)
“All of God’s children have God’s seal on them. In a word: all who have saving faith are sealed with the Holy Spirit. ‘God’s solid foundation stands firm, sealed with this inscription: “The Lord knows those who are his”‘ (2 Tim. 2:19). First, He authenticates us. We have been given authority to become sons of God (John 1:12). Second, He owns us. We are not our own; we are bought with a price (1 Cor. 6:20). Indeed, God ’set his seal of ownership on us’ (2 Cor. 1:22). Third, the seal of God on us guarantees our safety. ‘He will command his angels concerning you to guard you in all your ways’ (Ps. 91:11). Fourth, there is nothing greater than having the approval of one whose power, authority, and integrity matters. Timothy had Paul’s approval. ‘I have no one else like him’ …he ‘proved himself’ (Phil. 2:20, 22). Finally, our eternal destiny is sealed. Paul said, ‘Do not grieve the Holy Spirit of God, with whom you were sealed for the day of redemption’ (Eph. 4:30).
… As for those who have not experienced this [assurance of salvation]-but eagerly want it-Dr. Lloyd-Jones had this to say (quoting Thomas Goodwin)… Don’t give up. Hold God to His own Word. One should remind God of His own promise: Don’t give up ‘until you know you have the life of God in your soul…’” (R.T. Kendall, Holy Fire, Kindle Locations 1078-1079)