Passage
But ye believe not, because ye are not of my sheep.
John 10:26 (ASV)
Nearby Context
John 10:24 The Jews therefore came round about him, and said unto him, How long dost thou hold us in suspense? If thou art the Christ, tell us plainly.
John 10:25 Jesus answered them, I told you, and ye believe not: the works that I do in my Father`s name, these bear witness of me.
John 10:26 But ye believe not, because ye are not of my sheep.
John 10:27 My sheep hear my voice, and I know them, and they follow me:
John 10:28 and I give unto them eternal life; and they shall never perish, and no one shall snatch them out of my hand.
Study Lenses
The verse centers on "sheep" and "believe". It is saying that the verse draws attention to "sheep" and "believe", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 25's "Jesus answered them I told you and..." into verse 27's "My sheep hear my voice and I...", so "sheep" and "believe" belong inside that flow. In John context, the local focus is the identity of Jesus, new birth, eternal life, and belief and unbelief.
A plain takeaway is to answer the verse's own emphasis on "sheep" and "believe" with trust shaped by these words, not by a vague optimism outside the passage.