The mighty change that occurs with baptism by fire is neither permanent nor unconditional. It lasts as long as the conditions of repentance are maintained.
And whosoever doeth this, and keepeth the commandments of God from thenceforth, the same will remember that I say unto him, yea, he will remember that I have said unto him, he shall have eternal life, according to the testimony of the Holy Spirit, which testifieth in me. (Alma 7:16)
Maintaining this condition is called retaining a remission of your sins.
A remission of your sins can be retained as long as you maintain a broken heart and a contrite spirit. In other words, as long as you continue to hunger and thirst for God’s word, and you submit to it and live it as soon as you receive it, you will remain in the same state you entered into upon being born again.
Being born again is the first event in a process leading to eternal life, and not the culmination of obtaining eternal life. It is described in the scriptures as “entering the gate” or “starting on the path” to eternal life.
17 Wherefore, do the things which I have told you I have seen that your Lord and your Redeemer should do; for, for this cause have they been shown unto me, that ye might know the gate by which ye should enter. For the gate by which ye should enter is repentance and baptism by water; and then cometh a remission of your sins by fire and by the Holy Ghost.
18 And then are ye in this strait and narrow path which leads to eternal life; yea, ye have entered in by the gate; ye have done according to the commandments of the Father and the Son; and ye have received the Holy Ghost, which witnesses of the Father and the Son, unto the fulfilling of the promise which he hath made, that if ye entered in by the way ye should receive.
19 And now, my beloved brethren, after ye have gotten into this strait and narrow path, I would ask if all is done? Behold, I say unto you, Nay; for ye have not come thus far save it were by the word of Christ with unshaken faith in him, relying wholly upon the merits of him who is mighty to save.
20 Wherefore, ye must press forward with a steadfastness in Christ, having a perfect brightness of hope, and a love of God and of all men. Wherefore, if ye shall press forward, feasting upon the word of Christ, and endure to the end, behold, thus saith the Father: Ye shall have eternal life. (2 Nephi 31:17)
A person who is on the path to eternal life retains a remission of sins by keeping God’s commandments.
We know that whosoever is born of God sinneth not; but he that is begotten of God keepeth himself, and that wicked one toucheth him not. (1 John 5:18. See also 1 John 3:1-10)
When someone who has been born again sins, they remove themselves from the path to eternal life. They have failed to “endure to the end”:
And if they will not repent and believe in his name, and be baptized in his name, and endure to the end, they must be damned; for the Lord God, the Holy One of Israel, has spoken it. (2 Nephi 9:24)
Those who have left the path can reenter it the same way they did before: by entering in at the gate, or fully repenting of their sins, fully submitting to God, and being born again.
The sacrifice of Jesus Christ provides us with a way to be forgiven of the sins we have committed, submit to him fully, and receive a spiritual rebirth. After being reborn, we are given the rest of our lives to follow Jesus by living his commandments. Our lives become a probation, to test us to see if we will keep God’s commandments. “... there was a space granted unto man in which he might repent; therefore this life became a probationary state; a time to prepare to meet God...” (Alma 12:24) If we do, we will qualify to live with him. If we do not, we must repent and begin to live his commandments, or we will disqualify ourselves from dwelling with him.