In John 10:25,26 our Lord said to a group of religious pharisees, “…I told you, and ye believed not: the works that I do in My Father’s name, they bear witness of Me. But ye believe not, because ye are not of My sheep, as I said unto you.” He did not say, “You are not of My sheep, BECAUSE YOU BELIEVE NOT”. He said, “You believe not, BECAUSE YOU ARE NOT OF MY SHEEP”. Faith is not of ourselves, it is the gift of God. (Eph. 2:8) He will give it to all of His sheep. And in return, they will “hear (His) voice… and Follow (Him).” (v. 27)
Do you hear the voice of Christ our Great Shepherd in His word? Do you believe Him? Do you believe that He laid down His life for His sheep; All of His sheep; and only His sheep? Are you following Him?; looking to Him?; trusting in Him as your only hope of salvation before God? If so, then you are one of His sheep! You believe, BECAUSE YOU (already) ARE one of His sheep.