"born again" to me is simple... it means to be willing to let go of all your ideas and beliefs and start at square one. Everyone has their idea and belief of what God is or isn't. Mostly from what we are taught and how we are raised. In order to be as innocent as a baby we must be willing to let go of all of these and learn from square one. Nicodemus was taught from day one how to follow Jewish law and how to be a pharisee. Jesus was simply telling him that there was no way for him to be able or willing to understand Jesus' teaching unless he was first willing to separate himself from his current beliefs, even though he already admitted he knew Jesus was preforming signs and was a teacher from God.
How do we know what is true or not? Nicodemus was completely biblical and upheld the law. As are most christians today. However, Jesus' teachings were new and unbiblical at the time. So, was Nicodemus right, denying to follow Jesus?
I think people forget or don't realize that God is not a religion. Jesus didn't come to start a religion he came to stop one. God's teachings are there for the unrighteous. The righteous aren't righteous because they follow laws, they follow laws because they are righteous. In being righteous they hear God and know when it is time to do what God wants of them. Like Jesus said..." the wind blows where it wishes and you hear the sound of it, but can not tell where it comes from and where it goes. So is everyone who is born of the Spirit. " Nicodemus was not able to follow God on a whim when he was asked because his position in the church was more important to him. He didn't seek his self worth from God, he saught it from those around him looking up to him as a teacher. In order to follow Jesus he would have had to give all of that up. This is proven by Nicodemus' reactions to Jesus... he continually tries to debate Jesus on technical logical levels instead of hearing Jesus and accepting him.
It is a natural instinct to want to be right. How can one know he or she is right? You can't, but people still try. They think that if they get enough people around them believing as they believe that they must be right by popular vote. Its the main reason people preach christianity instead of following and living it. If you are born again and have let go, the truth is more obvious and easier to understand. It's easier to go against what you have been taught when the time calls for it and God calls for it. Who knows what became of Nicodemus... Jesus continues talking to him and preaches the most famous scripture of christianity.(john 3:16) Maybe he heard finally and was willing to listen. Maybe not... That is how I interpret being born again.
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Quran[2:62]Surely, those who believe, who are Jewish, Christian, and the converts; anyone who believes in GOD, and in the Last Day, and leads a righteous life, will receive their recompense from their Lord. They have nothing to fear, nor will they grieve.