Marvel not that I said unto thee, Ye must be born again.
Marvel not [do not be surprised, astonished] at My telling you, You must all be born anew (from above).
Marvel not that I said unto thee, Ye must be born anew.
Don’t be surprised that I said to you, ‘You must be born anew.’
You should not be amazed that I said to you: You must be born anew.