3:1 Now there was a man of the Pharisees named Nicodemus, a ruler of the Jews. 2 This man came to Jesus  by night and said to him, “Rabbi, we know that you are a teacher come from God, for no one can do these signs that you do unless God is with him.” 3 Jesus answered him, “Truly, truly, I say to you, unless one is born again  he cannot see the kingdom of God.” 4 Nicodemus said to him, “How can a man be born when he is old? Can he enter a second time into his mother's womb and be born?” 5 Jesus answered, “Truly, truly, I say to you, unless one is born of water and the Spirit, he cannot enter the kingdom of God. 6 That which is born of the flesh is flesh, and that which is born of the Spirit is spirit.  7 Do not marvel that I said to you, ‘You  must be born again.’ 8 The wind  blows where it wishes, and you hear its sound, but you do not know where it comes from or where it goes. So it is with everyone who is born of the Spirit.”
9 Nicodemus said to him, “How can these things be?” 10 Jesus answered him, “Are you the teacher of Israel and yet you do not understand these things? 11 Truly, truly, I say to you, we speak of what we know, and bear witness to what we have seen, but you  do not receive our testimony. 12 If I have told you earthly things and you do not believe, how can you believe if I tell you heavenly things? 13 No one has ascended into heaven except he who descended from heaven, the Son of Man.  14 And as Moses lifted up the serpent in the wilderness, so must the Son of Man be lifted up, 15 that whoever believes in him may have eternal life. 
16 “For God so loved the world,  that he gave his only Son, that whoever believes in him should not perish but have eternal life. 17 For God did not send his Son into the world to condemn the world, but in order that the world might be saved through him. (John 3:1-17 (ESV)
If I have told you earthly things and you do not believe, how can you believe if I tell you heavenly things? No one has ascended into heaven except he who descended from heaven, the Son of Man.
Trinity Sunday, A Sunday dedicated to the revelation of God as he is, three in one, triune, Father, Son and Holy Ghost. It is a doctrine we would not know if God had not revealed himself to us in this manner through his Son Jesus Christ, who indeed teaches us heavenly things. He alone qualified to do so, because he alone has ascended to heaven, he alone has descended from heaven, he alone, the Son of Man. And he reveals to us the nature of God, as he reveals to us the love of God in his sacrifice on the Cross. These are intimately connected for us, God being three in one, and our eternal salvation. For God so loved the World that he gave his only son, that whoever believes in him should not perish but have eternal life.
This of course is what Nicodemus had come to talk to Jesus about. The nature of salvation. Nicodemus had hang ups with what Jesus had to say, because Jesus tells him he has to be born again, born of water and the Spirit. What follows is a discourse on baptism, in which the triune God is first introduced to us, as water pours over our heads in the name of the Father and of the Son and of the Holy Spirit, and then of revelation. Nicodemus belonged to the Sanhedrin that would crucify Jesus, that had rejected the baptism of John. And to drive home this point, John says that after this Jesus went out into the country side to baptize, and John was baptizing at Aenon near Salim because water was plentiful there. Nicodemus is having a hard time with this, of what value could be water?
It’s the same sort of objection that is met today on any number of theological issues, really. The Trinity, Baptism, the Lord’s Supper, issues of sexual morality, the word of God. How can you know? This is the question. People instinctively know that God is beyond our reason, that he is unfathomable. I had a guy recently tell me this, and then immediately begin to tell me God couldn’t be who I said he was because that would be unreasonable. I kindly, and as gently as I could explained to him that he could not have his cake and eat it too. When he didn’t understand my meaning, I pointed out that if God is beyond our reason and unfathomable, and this was an agnostic more or less, if we are agreed on that, then he is in no place to tell me how God can’t be. It’s sort of what Jesus is getting at here when he says if I tell you earthly things and you do not believe, how can you believe if I tell you heavenly things?
The fact is we know so little. We like to think we are quite advanced and know so much more about the world than past generations. We figured out the pattern of the stars as it were. Our technology is incredibly advanced. We have a “scientific worldview.” Oh, but it is fun. What makes science fun, I mean truly fun, isn’t what we know, it’s exploring what we don’t know. A few minutes listening to a lecture by Tyson Neil deGrasse and you begin to learn how much we just don’t know. It sort of makes a person wonder then why he can be so full of the hubris he condemns in past generations as he makes his own wild claims about the possibility of God and so forth. We may know more about the nature of wind than Nicodemus did in his day, but is it not still a mystery to us? The nature of time and space that used to be so simple, and yet it has now been occupying the minds of the most brilliant physicists for the better part of a century. There is still much to know about this world. And yet we think we can tell God that we know him better.
We really aren’t any better than those who want to measure God according to first grade math of one plus one plus one equals three. Does it make sense that we should treat God as if he was as fathomable as beans on an amicus? The world wants to say, but it is just water, surely God doesn’t need water to save us. But it is just bread and wine, how can that be the body and blood of Jesus Christ? How can words, written on a page by men handed down over the centuries, how can that be the word of God, when it so badly contradicts our own human reason, our scientific knowledge? But then it makes sense that if we do not know earthly things, perhaps we are not in a place to contradict the Son of man, who was made man for our salvation, who walked on water, and even changed it into wine, who rose Lazarus from the dead, and three days after his own death rose again. God himself come into the world, not to condemn it, but to save it. God who died for our sins, and rose for our justification.
Now the peace of God that surpasses all understanding keep your hearts and minds in Christ Jesus our Lord. Amen.