Nicodemus is a Pharisee, a ruler of the Jews, a teacher of Israel. But he is in the dark and does not understand. He tries to come to Jesus by the Law instead of by faith, but it doesn’t work. He reasonably considers himself an expert in matters of religion; he’s evaluated Jesus on the basis of what he knows, and he’s reached a preliminary conclusion that is flattering and complimentary. Yet, for all of that, he is ignorant and naive. Jesus has to stop him in his tracks and take him to school: not for academic information, but to be entirely reborn as a new person.
You also are in the dark, conceived and born under the Law; and you cannot see the Kingdom of God — you cannot perceive or recognize it — except that you are born again, enlightened by the washing of water with the Word and Spirit of God in Holy Baptism. Otherwise, you would still have the same problem that Nicodemus did on the night when he first came to Jesus.
By your own natural reason and strength, you think you know what God is like, but you are wrong. You imagine that God must be like you; that He must think like you, and act like you, and deal with you in the way that you would deal with your neighbor. Not so. You suppose that you know what "spirituality" is, and what it ought to look like, but really you don’t have a clue.
You cannot recognize God when you see Him, and you would never have been able to find your own way to Him. You could never have ascended into heaven by any way or means of your own (though in your sin you presumptuously make the attempt). But Christ the Lord, your God, has descended from heaven to you, in order to raise you up with Himself in His Ascension.
By your first birth (of flesh and blood), you have inherited your parents’ sin and death, which blind you to all that pertains to God. It is only by the new birth of the Spirit (by Holy Baptism) that you have entered the Kingdom of God — through the Cross & Resurrection of Christ Jesus. Through Him, the promised Seed of Abraham, you have become a child of Abraham by faith.
All of this is the gracious good work of God for you, His gift; and yet, you could not recognize it, nor even receive it, by your own perception or insight — not by any ingenuity or understanding of yours. It becomes all the more impossible for you (and Nicodemus) to see or understand, when it comes down to the Sign that Jesus performs in the Hour of His Glory: in His Crucifixion. There He glorifies the Father’s Name, but He surely does not look like a teacher sent from God upon the Cross; far less does He there appear to be God Himself, manifested in the flesh; yet, so He is.
Indeed, it is by His Cross and Crucifixion, first of all, that He is lifted up for you, in order to atone for your sins, to call you to Himself, and to bring you with Himself back to the Father in heaven.
You are born again, through His death, unto life with God. There is no Resurrection or Ascension for you, except by the Cross of Christ. Only by the Cross and Passion of the Lord Jesus Christ are you set right with God and brought into harmony with Him.
Look to Christ, therefore, hung upon the Cross for your life and salvation. For all who look to Him in faith, all who believe and are baptized into Him, shall not perish but have everlasting life. Look to Him, and live. He has not come to judge you or condemn you, but to save you.
Still, none of this is within your own natural grasp. You could not see it, nor comprehend any of it, much less believe it. Nor can you even now by any will or wisdom of your own heart or mind.
But the Holy Spirit calls you by the Gospel, enlightens you with His gifts, sanctifies and keeps you in the true faith, unto the life everlasting. That is the essential key to everything, by which you enter the Kingdom of God through Christ Jesus, the incarnate Son. The Spirit reveals Him to you.
It is the Holy Spirit, by the Gospel, who fixes your eyes on Jesus, the Author and Perfecter of faith. Because He loves you, He lays Christ upon your heart with the Gospel, and He lays you upon the bosom of the Father in and with Christ Jesus.
So has He also given you the new birth of Holy Baptism.
The Church, therefore, the Lord’s own beloved Sarah, has thus become your Mother in Christ, having given birth to you from the womb of the font (by the Word and Spirit of God); so that, not only Abraham, but God Himself is now your Father, and you are His own dear child and heir. But you do not have the Father without the Mother. You do not have the Lord your God apart from His Bride, the Church. You do not have your Father’s eyes to see the Kingdom of God, unless you have your Mother’s ears to hear the Spirit's Voice in the Word of Christ.
The Holy Spirit is actively present and at work within the Church on earth, and He speaks the Gospel to you by such earthly ways and means. Here He is breathed upon you from the Cross of Christ in words of forgiveness, in the water and the blood. Do not suppose that you will lay hold of heavenly things apart from these earthly means. You won’t. You can’t. But the Holy Spirit performs His work upon you with earthly things that you can see and touch and handle and taste.
You cannot see the Spirit with your eyes, nor can you predetermine His comings and goings. Do not even try. But you do hear His Voice, because He calls you by the Gospel out of darkness into light, out of the nighttime of your sin and death and unbelief, into the Day of the Lord.
You have known His Voice in the waters of Holy Baptism, when He came down to rest and remain upon you in the bodily form of that Sacrament, and the heavens were opened to you.
You still hear the Spirit’s Voice in this very preaching of the Gospel, and in the spoken Word of Absolution, which is the free and full forgiveness of your sins, in Jesus’ name and for His sake.
So do you hear the Spirit’s Voice in that Word of Christ with which He bids you eat and drink His Body given, His Blood poured out, for you.
It is by this Word of Christ, the Voice of the Holy Spirit, that God the Father declares you to be righteous, His beloved and well-pleasing child.
And at the last, this same Voice of God, by which all things were created out of nothing, will raise your body from the grave (as Christ Himself is raised) and bring you into His Kingdom forever and ever. Amen!