Respectfully, that isn't really worded as a condition in that passage. It would be a condition if it said something closer to "You are my sheep if you hear my voice and follow me" which fits with a verse like: John 8:31 [NKJV] Then Jesus said to those Jews who believed Him, “If you abide in My word, you are My disciples indeed."
In this case, it reads more like a simple statement of fact about His sheep. Jesus has a personal relationship with his people (we hear His voice and He knows us) and because of that relationship, we follow Him (unlike the goats or wolves in sheeps clothing or those who are not His sheep).
John 10:26 [NKJV] But you do not believe, because you are not of My sheep, as I said to you.
Yes, believe means commit, trust, obey.
Those who believe, obey.
If you believe Jesus is your Lord, then you obey what he says.
Jesus qualifies what it means to be "His sheep" : My sheep hear My voice, and I know them, and they follow Me.
Hear in this verse means to listen and do what is said, hence the confirmation of "they follow me".
- That is what sheep do, they "follow" the Sheppard, and do what the Sheppard tells them to do.
Those that follow
for a while, and obey His voice
for a while,
then become lost, are likened to sinners who are lost and need to repent.
4 “What man of you, having a hundred sheep, if
he loses one of them, does not leave the ninety-nine in the wilderness, and go after the one
which is lost until he finds it? 5 And when he has found
it, he lays
it on his shoulders, rejoicing. 6 And when he comes home, he calls together
his friends and neighbors, saying to them, ‘Rejoice with me,
for I have found my sheep which was lost!’ 7 I say to you that likewise there will be more joy in heaven over
one sinner who repents than over ninety-nine just persons who need no repentance.
Luke 15:4-7
Those who believe, show the believe by following Him, and obeying His Voice, are qualified as Sheep, if they maintain their belief and continue to the end, not just for a while.
Judas obeyed and followed Jesus for 3 1/2 years, as a faithful disciple, and was then promoted to an apostle, in which he preached the Gospel to the lost, and was empowered to heal the sick and raise the dead, and cast out devils [the signs of those who believe] then became a traitor.
Example:
A shepherd goes to a far country to buy a herd of 100 sheep.
He purchases the sheep, and begins his journey back home.
On the way one of the sheep strays away and becomes lost, and wanders to become part of another herd.
When the shepherd arrives home, he counts his sheep and sees he only has 99 sheep.
How many sheep does the shepherd have?
JLB