"What happens when a person is born again"

The new birth is our first step into receiving eternal life, and entering into the Kingdom of God.

Acts 2:38 Peter replied, “Repent and be baptized, every one of you, in the name of Jesus Christ for the forgiveness of your sins. And you will receive the gift of the Holy Spirit.
When a person repents, it means he came to the conclusion that he is a sinner in need of salvation, and because of this conviction he turns to God, through water baptism, to ask God to cleans his conscience of all that guilt and shame that's been keeping him from God, and eternal life.
1 Peter 3:21 Baptism, which is symbolized by that water, now saves you also, not by removing dirt from the body, but by asking God for a clear conscience based on the resurrection of Jesus, the Messiah.
The forgiveness of sin is what cleanses the conscience, and the receiving of the Spirit is what changes us, and empowers us, to obey God. Ezekiel reveals to us what happens through water baptism.
Ezekiel 36:25-27 Then I will put clean water on you, and you will be clean. I will make you clean from all your unclean ways and from all your false gods. I will give you a new heart and put a new spirit within you. I will take away your heart of stone and give you a heart of flesh. And I will put My Spirit within you and cause you to follow My Laws and be careful to do what I tell you.
Through the act of water baptism, we are giving Jesus permission to come into our conscience, with the purifying fire of God, to cleans it with a surgical like precision.
Matthew 3:11-12 I indeed baptize you with water unto repentance, but He who is coming after me is mightier than I, whose sandals I am not worthy to carry. He will baptize you with the Holy Spirit and fire. His winnowing fan is in His hand, and He will thoroughly clean out His threshing floor, and gather His wheat into the barn; but He will burn up the chaff with unquenchable fire.
This is something the blood of bulls and goats could not do.
Hebrews 9:13-14 The blood of goats and bulls and the ashes of a heifer sprinkled on those who are ceremonially unclean sanctify them so that they are outwardly clean. How much more, then, will the blood of Christ, who through the eternal Spirit offered himself unblemished to God, cleanse our consciences from acts that lead to death, so that we may serve the living God!
We can only serve God with a clean conscience. It’s that clean conscience that keeps us spiritually alive, and connected to Jesus for eternal life. This is why it's so important to keep our conscience clear before God, and man.
Acts 24:15-16 I have hope in God, which they themselves also accept, that there will be a resurrection of the dead, both of the just and the unjust. This being so, I myself always strive to have a conscience without offense toward God and men.
Spiritual death is to be disconnected from eternal life. This happens when we harden our heart towards the saving work of God in our lives.
Hebrews 3:12-14 Beware, brethren, lest there be in any of you an evil heart of unbelief in departing from the living God; but exhort one another daily, while it is called “Today,” lest any of you be hardened through the deceitfulness of sin. For we have become partakers of Christ if we hold the beginning of our confidence steadfast to the end.
James 1:14-16 But each one is tempted when he is drawn away by his own desires and enticed. Then, when desire has conceived, it gives birth to sin; and sin, when it is full-grown, brings forth death. Do not be deceived, my beloved brethren.
1 Timothy 4:1-3 The Spirit clearly says that in later times some will abandon the faith and follow deceiving spirits and things taught by demons. Such teachings come through hypocritical liars, whose consciences have been seared as with a hot iron. They forbid people to marry and order them to abstain from certain foods, which God created to be received with thanksgiving by those who believe and who know the truth.
Spiritual death is not something irreversible. We can repent, be cleansed once again, and have our connection to eternal life restored. In other words, we can be grafted back into the vine.
1 John 1:9 If we confess our sins, He is faithful and just to forgive us our sins and to cleanse us from all unrighteousness.
Romans 11:20-23 Well said. Because of unbelief they were broken off, and you stand by faith. Do not be haughty, but fear. For if God did not spare the natural branches, He may not spare you either. Therefore consider the goodness and severity of God: on those who fell, severity; but toward you, goodness, if you continue in His goodness. Otherwise, you also will be cut off. And they also, if they do not continue in unbelief, will be grafted in, for God is able to graft them in again.
Luke 15:21-24 The son said to him, ‘Father, I have sinned against heaven and against you. I am no longer worthy to be called your son.’ “But the father said to his servants, ‘Quick! Bring the best robe and put it on him. Put a ring on his finger and sandals on his feet. Bring the fattened calf and kill it. Let’s have a feast and celebrate. For this son of mine was dead and is alive again; he was lost and is found.’ So, they began to celebrate.
The Father's arms are always open for our return, the problem is, some of us don't want to return.
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, and have tasted the good word of God and the powers of the age to come, 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.
If, and when, we fall into sin, don't let it grow to where it takes over your life, and harden your conscience, just acknowledge it as sin, and turn to God for that cleansing, and restoration. This is the part of God's work of salvation called, sanctification.
John 17:17 Sanctify them by Your truth. Your word is truth.
1 John 1:9 If we confess our sins, He is faithful and just to forgive us our sins and to cleanse us from all unrighteousness.
Matthew 18:21-22 Then Peter came to him and asked, “Lord, how often should I forgive someone who sins against me? Seven times?” “No, not seven times,” Jesus replied, “but seventy times seven!

How do you know if you’ve been born again? You will have a new hunger, and a thirst, for Gods righteousness.

Matthew 5:6 Blessed are those who hunger and thirst for righteousness, for they will be filled.

Your new birth will begin to show, because you will find yourself practicing God's righteousness, and loving other believers, which is something you never thought you would be doing.

1 John 3:10 So, now we can tell who are children of God and who are children of the devil. Anyone who does not live righteously and does not love other believers does not belong to God.

Why do people, who have been born again, have all these new feelings, convictions, and a change in their priorities? Because in Christ, you are a new creation, you become a new person.

2 Corinthians 5:17 Anyone who belongs to Christ has become a new person. The old life is gone; a new life has begun!

Amen...