He who has received his witness has set his seal to this, that God is true.

 (ii) But there may be another reason. The rabbis declared that the best time to study the law was at night when a man was undisturbed. Throughout the day Jesus was surrounded by crowds of people all the time. It may well be that Nicodemus came to Jesus by night because he wanted an absolutely private and completely undisturbed time with Jesus. 