Why did Jesus say to Nicodemus: "You must be born again"? It was certainly neither to encourage spiritual laziness nor to tempt him to try to produce it himself. We are just as unable to perform the second birth as we were the first. Rather, our Lord wanted him and us to realise our need of this great change and to seek the Spirit to do it for us. What then is the way forward? Jesus directs Nicodemus to the Old Testament incident when the sinning Israelites were bitten by snakes. When they repented, God told Moses to make a snake of brass, place it upon a pole in the middle of the camp and the dying Israelite who looked at it would be saved. Christ explains to Nicodemus: "So must the Son of Man be lifted up; that whosoever believeth in him should not perish, but have eternal life" (Jn.3:14-15). God, in His great love, has given His only begotten Son to die on the cross as a sacrifice to reconcile God and man. "He that believeth on the Son hath everlasting life" (Jn.3:36). Look to Him!
But how do I believe? Come to Him in prayer. Confess your sin and guilt. Plead with Him to save you. Put your trust in Christ and His saving work. Cast yourself upon Him. Give your heart and life to Him. Look away from your own righteousness to the Lord and His glorious work on Calvary. "As many as received him, to them gave he power to become the sons of God, even to them that believe on his name: which were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God" (Jn.1:12-13). Remember, the "whosoever" of John.3:16 means that this gospel is addressed to you.