IT WAS A DARK AND STORMY NIGHT: Well, maybe it wasn't stormy, but it was a dark night that Nicodemus came to find out who Jesus really was. Pay attention, however, as you read through John's gospel for his references to the night. Some will be more obvious to others, but John uses it to refer to the darkness of sin.
YOU CAN'T ENTER WHAT YOU DON'T SEE: In v5 Jesus tells Nicodemus that a person cannot enter the Kingdom of God unless he has been born again. This makes sense, for since you were born into a sinful nature as a child, you need to be reborn into the perfect righteousness that the comes through Christ. But earlier in v3, Jesus says a person cannot even see the Kingdom of God without being born again. The next time you notice the world berating Christianity, remember that people who haven't been born again can't see what you see.
YES, YOU'RE A BORN AGAIN CHRISTIAN: We use this phrase to describe a person who had a massive conversion experience in life, where one day they couldn't even see the Kingdom, but the next day they entered into it. Some of you have had that experience, but for most of us, we've never really had a noticeable conversion experience, so we don't think of ourselves as being born again. But we are. Just because you may not remember being born again doesn't mean you are not.
WHOSE LINE IS IT ANYWAY? Take a good look at your printed Bible. Notice all of the helps on the page that aren't words of scripture: chapter and verse numbers, footnotes, paragraph breaks and spaces between the words(!), quotation marks, and in some Bibles, even the words of Jesus are printed in red. None of those things are in the original Greek manuscripts. They've been added over the years to help us understand it in English, and a ton of work took place so that you can place a ton of trust in them.
But it's not always easy to determine what goes where. John 3:16 is a perfect example. Did Jesus speak those famous words, or are they commentary that John added? Different translations of the Bible come to different conclusions on that. Although determining these specifics makes for really interesting discussions, and casts the words in slightly different lights, we can fully trust what's written whether Jesus said it or John concluded it, because all of these words are fully inspired by the Holy Spirit.
For the record, I think the words are John's commentary, not Jesus' quotation, just as the words in v31-36 are likely John's commentary on what John the Baptist said in v27-30.
Follow the AAA Prayer Pattern:
ACKNOWLEDGE WHO GOD IS: For God so loved the world (v16)
ALIGN YOUR LIFE WITH GOD'S WILL: Ask God that you might live by the truth and come into the light (v21)