(John 10:15-16) “As the Father knoweth me, even so know I the Father: and I lay down my life for the sheep. And other sheep I have, which are not of this fold: them also I must bring, and they shall hear my voice; and there shall be one fold, and one shepherd.”
The different folds are the different nations of the world. Israel was the first nation that the Shepherd called His sheep out of, however not all of the blood linage of Abraham were called. Not all of any linage are called. He calls His sheep "out of" every kindred and tongue and nation of peoples (Rev.5:9). He calls the redeemed and His sheep whom He has bled and died for hear is voice and the come out to Him and then they continue to follow Him, (v. 4, 27).
(John 10:26-27) “But ye believe not, because ye are not of my sheep, as I said unto you. My sheep hear my voice, and I know them, and they follow me:”
These men were Jews and yet believed not “because” they were not His sheep. It does not say they were not His sheep “because” they believed not!