How does the Holy Spirit put His seal on a newly-baptized person?
The idea that the Holy Spirit acts supernaturally to put a seal on a baptised believer is a misunderstanding of scripture. The Holy Spirit is not a person, the Holy Spirit is the power of God. The twelve apostles were baptised with the Holy Spirit at Pentecost. One of the powers they received was that of bestowing Holy Spirit gifts on baptised believers by the laying on of their hands. Those who received a gift of the Holy Spirit by the laying on of the apostles’ hands could not give Holy Spirit gifts to others. This is clearly seen in Acts chapter 9 when Philip converted and baptised some Samaritans. Philip couldn’t give Holy Spirit gifts to them. It required Peter and John to travel from Jerusalem to lay hands on them.
First century believers received gifts of the Spirit as promised.
Acts 2:38 Then Peter said to them, "Repent, and let every one of you be baptized in the name of Jesus Christ for the remission of sins; and you shall receive the gift of the Holy Spirit.
But they received a gift by the laying on of the apostle’s hands.
Ephesians 1:13 In Him you also trusted, after you heard the word of truth, the gospel of your salvation; in whom also, having believed, you were sealed with the Holy Spirit of promise
When the apostles died, Holy Spirit gifts were no longer available. The only way that we can be influenced by the Holy Spirit is by reading, understanding and obeying the Gospel preached by Jesus and his apostles.
The Bible was inspired by the Holy Spirit.
2 Peter 1:21… holy men of God spoke as they were moved by the Holy Spirit.
Jesus told his disciples:
John 6:63 It is the Spirit who gives life; the flesh profits nothing. The words that I speak to you are spirit, and they are life.
The Holy Spirit is in the words.
John 15:3 You are already clean because of the word which I have spoken to you.
If we ensure that the words of Jesus Christ abide in us, then we are ‘sealed’.
1 John 2:24 Therefore let that abide in you which you heard from the beginning. If what you heard from the beginning abides in you, you also will abide in the Son and in the Father.
2 Corinthians 1:22 who also has sealed us and given us the Spirit in our hearts as a guarantee.
Spirit in our hearts is different from Holy Spirit gifts – it denotes a changed way of thinking – we must change our natural way of thinking to the way that Jesus commands us. This is how we are ‘born again’ of the Spirit. However, we can still grieve the Spirit of God by disobedience.
Ephesians 4:30 And do not grieve the Holy Spirit of God, by whom you were sealed for the day of redemption.
If we subsequently turn away from the Gospel, then we become ‘unsealed’ as it were. Even those in the first century who had received Holy Spirit powers could still fall away.
Hebrews 6:4-6 For it is impossible for those who were once enlightened, and have tasted the heavenly gift, and have become partakers of the Holy Spirit, 5 and have tasted the good word of God and the powers of the age to come, 6 if they fall away, to renew them again to repentance, since they crucify again for themselves the Son of God, and put Him to an open shame.
Paul says of himself:
1 Corinthians 9:27 But I discipline my body and bring it into subjection, lest, when I have preached to others, I myself should become disqualified.
James 1:22 But be doers of the word, and not hearers only, deceiving yourselves.
I hope you find this helpful.