Who is the thief in John 10 and what does he steal?

Let’s begin by looking at the passage as a whole:

John 10:1 “Truly, truly, I say to you, he who does not enter by the door into the fold of the sheep, but climbs up some other way, he is  a thief and a robber.
John 10:2 “But he who enters by the door is  a shepherd of the sheep.
John 10:3 “To him the doorkeeper opens, and the sheep hear  his voice, and he calls his own sheep by name and  leads them out.
John 10:4 “When he puts forth all his own, he goes ahead of them, and the sheep follow him because they know  his voice.
John 10:5 “A stranger they simply will not follow, but will flee from him, because they do not know  the voice of strangers.”
John 10:6 This  figure of speech Jesus spoke to them, but they did not understand what those things were which He had been saying to them.
John 10:7  So Jesus said to them again, “Truly, truly, I say to you, I am  the door of the sheep.
John 10:8 “All who came before Me are  thieves and robbers, but the sheep did not hear them.
John 10:9 “ I am the door; if anyone enters through Me, he will be saved, and will go in and out and find pasture.
John 10:10 “The thief comes only to steal and kill and destroy; I came that they  may have life, and  have it abundantly.
John 10:11  “ I am the good shepherd; the good shepherd  lays down His life for the sheep.
John 10:12 “He who is a hired hand, and not a  shepherd, who is not the owner of the sheep, sees the wolf coming, and leaves the sheep and flees, and the wolf snatches them and scatters them.
John 10:13 “He flees because he is a hired hand and is not concerned about the sheep.
John 10:14 “ I am the good shepherd, and  I know My own and My own know Me,
John 10:15 even as  the Father knows Me and I know the Father; and  I lay down My life for the sheep.
John 10:16 “I have  other sheep, which are not of this fold; I must bring them also, and they will hear My voice; and they will become  one flock with  one shepherd.

Notice that in this context Jesus is speaking figuratively (v.6) and metaphorically to make a point. Jesus is not talking about literal sheep or shepherds, nor is He talking about literal thieves stealing things. He is speaking about the Kingdom of God and how Jesus protects believers from all things, including from those who make false claims and attempt to deceive Christ's followers.

First, Jesus says that He is the door, the one way by which we may enter into eternal life. Before Jesus came, there were others who came claiming to be the Messiah, but these false messiahs were merely "thieves" trying to steal Christ's glory. Because they were not truly the Messiah, God's children (i.e., the sheep) did not hear them.

So notice that the thief in this passage is not the Devil. In this analogy, Jesus says that the earlier false messiahs were the thieves. Certainly, these false prophets were working under Satan's direction, but it is incorrect to say that the thief in John 10:10 is the Devil. In fact, it is the one who falsely claims to be Christ.

Secondly, notice that this is not a passage talking about when people die or how people die or if the Devil can cause someone to die or any of those things. This passage is not talking about living or dying at all. To take this passage and use it to support the notion that Satan is taking the lives of children is grossly improper, completely inaccurate, and a woefully ignorant use of scripture. To repeat - Jesus was not talking about anyone dying.

Instead, Jesus was talking about salvation. He was explaining that when the real Messiah arrived on earth, the people appointed to salvation heard His voice and followed Him into eternal life. They followed Him because God's people will always know the truth about God. Others have come into the world trying to deceive people into following them as if they were Christ (these were the thieves), but they could not steal Jesus' sheep. His sheep know Him and will follow Him.