“The same came to Jesus by night, and said unto him, Rabbi, we know that thou art a teacher come from God: for no man can do these miracles that thou doest, except God be with him.”
He came to Jesus at night and said, 'Rabbi, we know you are a teacher who has come from God; for no one could perform the signs you are doing if God were not with him' — Nicodemus' nocturnal visit initiates the Gospel's light/darkness motif; spiritual blindness is suggested by temporal darkness. His confession of Jesus as God-sent teacher and his recognition of signs testifies to growing faith, yet John will show such sign-based recognition as incomplete. The plural "we know" suggests Nicodemus represents institutional religious authority's tentative openness.
Church Fathers on John 3:2
He had said above that, when He was at Jerusalem many believed in His Name, when they saw the miracles which He did. Of this number was Nicodemus, of whom we are told; There was a man of the Pharisees, Nicodemus, a ruler of the Jews.
His rank is given, A ruler of the Jews; and then what he did, This man came to Jesus by night: hoping, that is, by so secret an interview, to learn more of the mysteries of the faith; the late public miracles having given him an elementary knowledge of them.
and therefore he came in the night, being afraid to come in the day. Of such the Evangelist speaks elsewhere, Nevertheless, among the chief rulers also many believed on Him; but because of the Pharisees they did not confess Him, lest they should be put out of the synagogue.