3:1-5 Nicodemus is a Pharisee and comes to visit Jesus at night. He tells him they know God is with him. This indicates that more than one person thinks this, but Nicodemus is the only person willing to go to him and say this. So he obviously has some guts to go against the grain and see Jesus. Visiting him at night could suggest a desire for an intimate conversation away from the crowds. Nicodemus is an educated man who is very aware of how these things work. To get the best information, it needs to be more of a one on one conversation. Jesus doesn't wait for a question. He tells him it's more than just realizing who I am. He puts it in plain words and not a parable. As I said, Nicodemus is an educated leader in Israel. He shouldn't need those extra helps. However, he still doesn't get it. Upon further explanation, Jesus refers to water and Spirit. It could be physical and spiritual birth or spiritual birth and baptism. Either way Jesus is telling him how to be born again.
3:6-8 Jesus continues to elaborate on the idea and hits on the idea that those of the Spirit don't make sense to those without the Spirit. There are going to be those that don't get why we do what we do. They might even be against what you are doing. So those of the Spirit may have to separate from those without it or at least distance yourself from those without it.
3:9-15 Nicodemus still doesn't get it and Jesus is amazed. So he tells it to him straight again. Paraphrasing: "If you don't believe something as small as giving sight to the blind, how can you believe something as large as salvation of a soul?" Don't we know people who have turned their backs on God because he didn't give them what they wanted when they wanted it. How can we be prepared for what God wants to give us when we are putting restrictions on him like in a time period or it has to be done a certain way? We must stop waiting on God to make himself more like us. We need to make ourselves more like God.
3:16 Probably the most famous verse in the Bible and rightly so. In a few simple words, Jesus sums it all up for us. But look at the power of the words he uses. The word believe in this case means "to place confidence in". It is what we say when we are talking to a friend and we say "I believe you." It is more than just I know this. It is I know it and I am compelled to act on that knowledge. When we say "I believe you" to a friend, those are powerful words. We are saying we have confidence in who they are and what they stand for. We are placing our trust and faith in them with the thing they are saying. This is what we need to do with Jesus. He also mentions eternal life. Can we conceive of this? If we put our confidence in him, we will have eternal life. And not a life like on this earth, it is "a life active and vigorous." and "the absolute fullness of life."
3:17-21 Then Jesus follows with a discussion of Light and Dark. What captures me about this discussion is that those in Darkness focus on their actions. It is selfish. It is all about that person. In the Light, it is not about individual action. It is God. It is what God has done. I am just the vessel. In my personal opinion, this is the biggest failing of Christians today. There is an unwillingness to step into the light. Something that sets Christians apart is our willing to say, I'm sorry. I messed up. Not God messed up, but I did. People in the Light should be willing to analyze themselves and say "This thing is too much about me. I need to give this to God and apologize to him and others for holding on to it." It is this that so many of us are missing. I am not exempting myself here. I am just as guilty of it as anyone. It is a process, but so is our Christian walk. It is something that we have to keep trying to get better at.
Overall, this whole passage is more than just verse 16 that we focus on. Jesus explains what to do to get to heaven (5), why you want to(16), and what to do between here and heaven(21). There is so much packed into these verses it is amazing how much of it seems to be overshadowed by verse 16. Praise God Nicodemus had the courage to ask these questions and the education to enough to get a straight answer.