I will ask the Father to send you the Advocate; the Holy Spirit; to be with you forever—
John 14:16
To all who have known the truth; which abides in us and will be with us forever:
I agree, once we receive the Holy Spirit we are sealed with Him, but Paul makes it clear in Ephesians 4:17-30 that we can grieve the Holy Spirit and continues on into Ephesians 5:1-6 to tell us that even people who are sealed with the Holy Spirit can once again become “sons of disobedience” and lose their inheritance in heaven.
“So this I say, and affirm together with the Lord, that you walk no longer just as the Gentiles also walk, in the futility of their mind, being darkened in their understanding, excluded from the life of God because of the ignorance that is in them, because of the hardness of their heart; and they, having become callous, have given themselves over to sensuality for the practice of every kind of impurity with greediness. But you did not learn Christ in this way, if indeed you have heard Him and have been taught in Him, just as truth is in Jesus, that, in reference to your former manner of life, you lay aside the old self, which is being corrupted in accordance with the lusts of deceit, and that you be renewed in the spirit of your mind, and put on the new self, which in the likeness of God has been created in righteousness and holiness of the truth. Therefore, laying aside falsehood, speak truth each one of you with his neighbor, for we are members of one another. Be angry, and yet do not sin; do not let the sun go down on your anger, and do not give the devil an opportunity. He who steals must steal no longer; but rather he must labor, performing with his own hands what is good, so that he will have something to share with one who has need. Let no unwholesome word proceed from your mouth, but only such a word as is good for edification according to the need of the moment, so that it will give grace to those who hear.
Do not grieve the Holy Spirit of God, by whom you were sealed for the day of redemption.”
Ephesians 4:17-30 NASB1995
According to this passage we can still grieve the Holy Spirit. Now look what he says in the beginning of the next chapter. Notice that he begins with the word “Therefore” which indicates that he is expanding on what he just said at the end of chapter 4.
“Therefore be imitators of God, as beloved children; and walk in love, just as Christ also loved you and gave Himself up for us, an offering and a sacrifice to God as a fragrant aroma.
But immorality or any impurity or greed must not even be named among you, as is proper among saints; and there must be no filthiness and silly talk, or coarse jesting, which are not fitting, but rather giving of thanks. For this you know with certainty, that no immoral or impure person or covetous man, who is an idolater, has an inheritance in the kingdom of Christ and God. Let no one deceive you with empty words, for because of these things the wrath of God comes upon the sons of disobedience.”
Ephesians 5:1-6 NASB1995
Right here Paul tells these Ephesians who have been “sealed with the Holy Spirit” that immorality must not be named among them otherwise they will have no inheritance in the kingdom of God and that for this reason the wrath of God comes upon the sons of disobedience.
Furthermore as I already pointed out the Galatians had been severed from Christ and had fallen from grace according to Galatians 5:4. You can’t be severed from Christ if you’ve never been joined to Him and you can’t fall from grace if it has never been bestowed upon you. And I also pointed out that Paul specifically said that these fallen Galatians had received the Holy Spirit according to Galatians 3:1-5.
“You foolish Galatians, who has bewitched you, before whose eyes Jesus Christ was publicly portrayed as crucified? This is the only thing I want to find out from you: did you receive the Spirit by the works of the Law, or by hearing with faith? Are you so foolish? Having begun by the Spirit, are you now being perfected by the flesh? Did you suffer so many things in vain if indeed it was in vain? So then, does He who provides you with the Spirit and works miracles among you, do it by the works of the Law, or by hearing with faith?”
Galatians 3:1-5 NASB1995
So again this is another indication that receiving the Holy Spirit doesn’t guarantee salvation. The only thing that guarantees salvation is remaining in Christ. So yes once we receive the Holy Spirit He will remain with us even if we apostatize and He will always be urging us to repent but if we continue to ignore Him we will not receive salvation if we don’t repent before we die.