Regeneration is a secret act of God in which He imparts new spiritual life to us. It is not merited or deserved in any way by those who receive it, and it is completely monergistic- that is, brought about completely by God. In other words, you don’t have any part in your regeneration.
In sanctification, for example, you do get to play a part. It isn't completely your work, but you get to participate in it by making decisions, repenting, using the spiritual disciplines, etc. But regeneration is not like that- it is something only God can accomplish (Titus 3:5-6, Ephesians 2:4-9).
In regeneration, God acts on the inner man, replacing deaf ears that cannot hear and blind eyes that cannot see and a heart of stone that cannot believe with spiritual heart and eyes and ears that hear and see and believe the truth of the gospel.
A great passage that helps us understand regeneration is 1 John 5:1-5.
"Everyone who believes that Jesus is the Christ has been born of God, and everyone who loves the Father loves whoever has been born of him. By this we know that we love the children of God, when we love God and obey his commandments. For this is the love of God, that we keep his commandments. And his commandments are not burdensome. For everyone who has been born of God overcomes the world. And this is the victory that has overcome the world—our faith. Who is it that overcomes the world except the one who believes that Jesus is the Son of God?" 1 John 5:1-5
Here are several important observations about regeneration
1. Regeneration Precedes Faith. (v1)
John writes, “Everyone who believes that Jesus is the Christ has been born of God.” In the original language, "believes" is present and active. The next phrase is "has been born of God." That’s perfect passive indicative. Perfect means it is an accomplished or completed action, and passive means the subject isn’t doing the action but is the recipient of the action. John writes that those who believe now have already been regenerated- born of God.
The alternative view is to say that we place our faith in Christ first and then we are regenerated. Not only does that conflict with what John says here, but also what we read in Ephesians 2. It would mean that one who is spiritually dead can accomplish a spiritual good on his own. The Ephesians 2 passage goes on to say “by grace you have been saved through faith. And this is not your own doing; it is the gift of God, not a result of works, so that no one may boast.” So, God must work on the spiritually dead man before he has the capacity to believe or respond in faith.
2. Regeneration changes our identity. (v1-2)
Regeneration means that we belong to a family of people who are also born again. This family is marked by love that runs two directions: If we love God, we love those who are born of Him. Likewise, we experience love from others who have also been born of God. But don’t think of this ‘fruit of regeneration’ as some kind of spiritualized hippie commune. Verse three defines love as obedience. This love is fierce. It has teeth. It covers a multitude of sins, yes. But it also calls for accountability. It instructs, gives rebuke, and both exerts and submits to authority.
We’ll learn more about this when we get to the topic of adoption, but those who have been regenerated belong to a new, spiritual family. What binds them together is greater than any of their former worldly or fleshly differences.
3. Regeneration changes what we love. (v2-3)
Those who are born of God obey his commandments, and keep his commandments. But notice the change of heart in verse three: His commandments are not burdensome. The unregenerate see God’s commandments as condemning, judgmental, a list of "must-dos" and "can-nots". But the one whose heart has been renewed by the washing of regeneration loves to obey. Listen to David in Psalm 19 “The decrees of the LORD are true, and righteous altogether. More to be desired are they than gold, even much fine gold; sweeter also than honey and drippings of the honeycomb.” And again, in Psalm 40:8 “I delight to do your will, O my God; your law is within my heart.” The regenerate begin to love what God loves, and hate what God hates.
4. Regeneration gives us assurance. (v4-5)
John says that the one who has bee born of God overcomes the world. Overcome means to conquer or to have victory in conquest. It’s the Greek word nike. Interestingly, it’s present tense. Those who have been regenerated not only will overcome the world… they are overcoming now. Doesn’t that one little detail make an enormous practical difference? The world seems to weigh on us so heavily, we often look only to a future relief. But if you’ve been born again, you’re an overcomer. You are able to have victory now. Not because of something you’ve done, but because of what God has done on your behalf.
5. Regeneration is evidenced by faith. (v5)
John sets up an equivalency here between the one who has been born of God and the one who believes. We've seen that regeneration must come first, but it necessarily brings about faith in Christ.
That’s important for 2 reasons.
First, it’s a reminder that we can’t separate the various facets of salvation completely. We can talk about regeneration and justification and sanctification as separate things. But God doesn’t work them out in such a compartmentalized way. We can say regeneration logically precedes faith, but we can’t say regeneration saves apart from faith in Christ. No one is saved apart from faith in Christ. So here in the text, John reminds us that the two are inseparable.
Second- Since regeneration is a required part of salvation, how does a person know if they are truly "born of God?" I think the best barometer we can use is this: have you responded to the gospel by placing your faith in Christ? Have you seen yourself as dead in sin apart from him- and that your only hope is Him and Him alone? That can’t happen unless God has caused you to be born again. John 1:12-13 reads, “But to all who did receive him, who believed in his name, he gave the right to become children of God, who were born, not of blood nor of the will of the flesh nor of the will of man, but of God.” If you repent and believe- you are born again.