The wind blows where it listeth, and thou hearest the sound thereof, but canst not tell whence it cometh, and whither it goeth: so is every one that is born of the Spirit. John 3:8.
A man who was a great scholar came to Jesus one night. He was a teacher, an intellectual, a thinker. He came to Jesus and said, "I notice that You're a great teacher. And I'm not so bad myself. Why don't we have a discussion?" But Jesus said, "What you need is to be born again."
Nicodemus had been worshiping something other than God. But he was drawn to Jesus. He came to have a discussion with Jesus. He didn't fully realize his need, and when Jesus said, "Except a man be born again, he cannot see the kingdom of God" (John 3:3), Nicodemus didn't understand. He proved that the unconverted man doesn't comprehend spiritual things, for he said, "How can a man be born when he is old?" It is only through the regenerating work of the Holy Spirit that we can even understand about salvation by faith in Jesus, which is what the "kingdom of God" refers to (Christ's Object Lessons, p. 62).
Jesus gave to Nicodemus that night His clearest presentation on the new birth. But was Nicodemus born again that night? The evidence we have is that he walked away through the darkness, pondering, thinking, wondering. For three years Jesus let the seed He had sown do its work. The new birth comes at the proper time for each person, and not even Jesus rushed the timetable. The timetable is not a clock or some number of years. It has to do with conditions. With some people the conditions necessary are fulfilled very quickly. For others, it may take a lifetime before they get fed up with life apart from God. For Nicodemus it took three years. But at least by the time of the crucifixion Nicodemus was able to accept the work of the Holy Spirit in regeneration. One of his first acts, along with Joseph of Arimathea, was to provide a decent burial for Jesus. This rich man became poor, and was ridiculed by his former friends, because of his loyalty to Jesus. But once Nicodemus had surrendered to the regenerating work of the Holy Spirit, he was willing to become poor, because of love for the One who became poor in our stead so that we, through His poverty, might become rich.