Question: Once a person is sealed by the Holy Spirit, can this seal be revoked?
Response: The question of the sealing of the Holy Spirit is indeed one of those concepts used by adherents of "eternal security" to prove their position. I am always reluctant to discuss this issue, but it is an important one (it will be given a detailed treatment in the upcoming Bible Basics 5: Pneumatology: the Biblical Study of the Holy Spirit). I am overjoyed to be the child of a loving and merciful God who has forgiven me so much and who sent His own dear Son to die for me that I might be forgiven all my offenses and have all my sins blotted out so that I might be saved. So there should be no doubt where I am coming from (and there is no doubt from scripture about God's desire that all be saved: Jn.3:16; cf. Ezek.18:23; Matt.18:14; Jn.12:47; 1Tim.2:4; 2Tim.2:24-26; 2Pet.3:9).
But while many are invited, few accept:
For those invited [to salvation] are many, but those chosen [for salvation] are few.
The road is narrow and the gate strait:
"How narrow the gate and how constricted the road which lead to life! And those who find it are few."
And only the seed sown in good ground bears fruit to eternal life:
And he who was sown on the rocky places, this is the one who hears the Word and immediately receives it with joy. He (i.e. his faith; cf. Lk.8:13) has no roots, however, but lasts only a short time. So when tribulation or persecution occurs on account of the Word, he is immediately tripped up (cf. Lk.8:13: "becomes apostate").
Specifically on the sealing of the Spirit, this is referring to the fact that all believers in Jesus Christ have the Holy Spirit dwelling in them, and this indwelling presence is therefore a "mark" that we who have put our faith in Jesus Christ are definitively now the property of God Himself. "Sealing" is thus an analogy used by Paul to express a truth about the present state of all believers in Jesus Christ. The analogy uses a well-known practice in the ancient world of rolling up a document or closing up a container (like a jar) then affixing a wax seal that is then marked with a person's signet ring (they were unique like our signatures). The seal of course could be broken easily enough, but once broken could not be reconstructed, so that few would venture to violate a seal, especially if the seal were that of a powerful person. Breaking God's seal, of course, is the height of temerity, so that our sealing by the Spirit is a comfort and a guarantee that nothing from the outside can come between us and our reward, between us and our resurrection, between us and our eternal life - nothing can make God loosen His grip on us, and no one on heaven and earth is capable (through courage or ability) to break His seal on us:
Now the One who has given us security in regard to Christ together with you and who has anointed us (i.e., with the Spirit) is God - [Yes, He] has also sealed us and given us His pledge of the Spirit in our hearts.
2nd Corinthians 1:21-22
In [Christ] you also when you heard the Word of truth, the good news of your salvation, in whom [I say], when you believed, you were sealed by the Spirit of promise, the Holy [Spirit], who is a pledge of our inheritance for redeeming its preservation (i.e., safeguarding our resurrection and reward in every way), to the praise of His glory.
And do not grieve the Holy Spirit of God with whom you were sealed for a day of redemption.
What these three "sealing" passages all assume, however, as do all the passages of scripture which reassure us of God's love, God's mercy, and God's faithfulness, is that we will continue in our faith, that we will continue faithful, that we will continue to follow Jesus. There is nothing in this analogy of the Spirit within us with whom we have been baptized at the point of faith in Christ, that good Spirit who indwells us, guides us and comforts us and acts as a pledge and a seal that we are God's own possession in Jesus Christ, there is nothing in the analogy, I say, that in any way removes the fact of our continued free will in this life or that removes our responsibility to follow Jesus in the way He has called us to do. Many are called but few are chosen.
Some would say that it is in some sense an academic, theological question as to whether those who fall away ever fit into this category of "the sealed" in the first place, or whether they did but were "unsealed" by their own efforts. Some would say that it is entirely academic, as I say, because unless and until we fall away, we imagine ourselves to be sealed (and I would say that we are), and once we do fall away if we do, then we are not sealed if we ever were (and I would say we were). The problem with this, from my point of view, is that by preaching "once saved always saved" we strip away a good deal of biblical motivation (deliberately placed in scripture) to walk prudently, righteously, and in a godly fashion in this life (Tit.2:12). Indeed, with this (false) doctrine we proclaim that a person can "do whatever they want", and while it may result in pain in time and loss of reward in eternity, it will not affect salvation. This is utter nonsense. We rejoice to take comfort in all the scriptures which proclaim our security in Jesus Christ (and the sealing of the Spirit is a great source of comfort and a solid pledge of security), but we have to understand that our security extends just as far as our faith and not farther; if we abandon our faith, we vacate our security, and nothing could be more horrible to contemplate than that. Yet in the future, a not so distant one by my scriptural calculations, a large section of the Church will fall into apostasy, and if we are not sure both of our faith and of the importance of holding true to it, such misguided efforts at false comfort are likely only to embolden those in danger of falling away from the faith.
I have written rather extensively on this topic. Here are some links you may find helpful:
The False Doctrine of Absolute Eternal Security III
Three Doctrines that threaten Faith (in Peter # 27)
Eternal Security (in Peter #21)
Eternal Security and "sinless perfection"
Eternal Security and "salvation by works".
For some related issues on seals and the Holy Spirit, please see:
Bible Basics 5: Pneumatology
The Seven Seals: Revelation 6:1-17
The Restraining Ministry of the Holy Spirit
The Holy Spirit (in BB1: Theology)
The Holy Spirit: Blasphemy against, Restraining Ministry, and Gender.
The Filling of the Holy Spirit
In the Name of the One who died for us that we might – through the perseverance of our faith in Him – live forever with Him, our Lord and Savior Jesus Christ.