The first lesson each believer in Christ should learn is that immediately upon believing he is given everlasting life. Referring to this fact Ephesians 1:13,14 says:
“In whom ye also trusted, having heard the word of truth, the gospel of your salvation: in whom also having believed, ye were sealed with that Holy Spirit of promise.”
Mark well, the believer is not sealed by the Holy Spirit, but “with” the Holy Spirit. The Spirit Himself is the seal. Every sincere believer in Christ, then, should rejoice in an accomplished redemption and rest in the fact that the Holy Spirit will keep him eternally safe.
But while we cannot lose the Holy Spirit we can, and often do, grieve the Holy Spirit, as we read in Eph. 4:30. This is why we are told in Rom. 8:26 that the Spirit “helpeth our infirmities” and makes intercession for us, that we might live lives which please and honor God.
The wonderful fact is, however, that “nothing,” not even an aggrieved Spirit shall “separate us from the love of God” (Rom. 8:38,39). Thus in the same breath with which the Apostle exhorts us not to grieve the Spirit he again reassures us that this same Spirit keeps us eternally safe:
“And grieve not the Holy Spirit of God, whereby ye are sealed unto the day of redemption” (Eph. 4:30).
Does this encourage careless living? Those who think so have missed the whole point of Paul’s appeal. The Apostle does not warn the believer that if he grieves the Spirit he will be lost. Rather, in grace he exhorts:
“Do not grieve the very Spirit who in mercy and love has sealed you as forever His own. Do not repay such love with such ingratitude.” source