You said this person believed the Gospel (i.e. Done good) which also means this person obeyed the Gospel.
Those are your words.
Those who believe the Gospel, obey the Gospel.
The Gospel: Repent for the kingdom of God is at hand.
Repent means to turn to God.
If you are called to repent, ie turn to God, then by default you are called to turn away from Satan as your lord.
If you believe the kingdom of God is at hand, then you obey the command to repent, which is to confess Jesus as Lord.
By this we are forgiven of our sins, and transferred out of the domain of darkness, into the kingdom of His Son.
This is what Jesus commissioned Paul to do.
15 So I said, ‘Who are You, Lord?’ And He said, ‘I am Jesus, whom you are persecuting. 16 But rise and stand on your feet; for I have appeared to you for this purpose, to make you a minister and a witness both of the things which you have seen and of the things which I will yet reveal to you. 17 I will deliver you from the Jewish people, as well as from the Gentiles, to whom I now send you, 18 to open their eyes, in order to turn them from darkness to light, and from the power of Satan to God, that they may receive forgiveness of sins and an inheritance among those who are sanctified by faith in Me.’ Acts 26:15-18
- in order to turn them from darkness to light, and from the power of Satan to God, that they may receive forgiveness of sins.
Jesus is now our Lord, and we are to obey Him, as Lord.
Loving and forgiving people is what He commands us to do.
3 Now by this we know that we know Him, if we keep His commandments. 4 He who says, “I know Him,” and does not keep His commandments, is a liar, and the truth is not in him. 1 John 2:3-4
It's not optional.
Can we ourselves who are saved through faith, disobey this command to love and forgive, instead choose to hate and harbor unforgiveness.
14 We know that we have passed from death to life, because we love the brethren. He who does not love his brother abides in death. 15 Whoever hates his brother is a murderer, and you know that no murderer has eternal life abiding in him.
1 John 3:14-15
3 Now by this we know that we know Him, if we keep His commandments. 4 He who says, “I know Him,” and does not keep His commandments, is a liar, and the truth is not in him. 1 John 2:3-4
I know Him, means you are claiming you are joined to Him, and are in Him where eternal life is.
JLB