That is, our Lord was not speaking to Nicodemus only, but to all who are in the same spiritual condition as Nicodemus. Regeneration is a moral necessity. The reason men are immoral is because they are separated from the life of God, which life is one of righteousness and holiness. In the New Birth, the Spirit of God changes an individual by taking up residence. Because of the indwelling of the Spirit, one is drawn toward holiness, righteousness and right conduct.
Regeneration is a mental necessity.
He that is dead in sin is dead toward God. Dead persons cannot serve the living Lord, they must be made alive. This is precisely what the New Birth accomplishes. He that is regenerated, or born from above, is made alive to God. Only a regenerated person can know God's will.