The Gate

The Thief
Breaking glass, picking locks and sneaking through windows are ways that a thief usually gains entry into forbidden places.  Most people lock their doors, set alarms or take precautions against intruders, however, we've learned through other people's misery that those measures don't always work.

Using a door or gate as an entrance is the standard—the robber has no approved access so he must figure out another way.  That's why when a neighbor sees someone climbing over walls or through windows, he can be pretty sure that something illegal is underway.

The Blind
In John Chapter 9, Jesus healed a man who was blind from birth.  When the man was questioned by the Pharisees about what had happened, he admitted he didn't know how Jesus had done it, but that he must be some kind of prophet, since no ordinary man was ever able to do such things.  The man was dismissed by the leaders as a fool and a sinner.

When Jesus was informed, He tracked down the man and simply told him who He was, and asked if he believed.  The man proclaimed his belief and worshipped Him.  Jesus used this opportunity to point out that the spiritual blindness of the religious was far worse than physical blindness.  And then, He proceeded to use the imagery of shepherding to make sure everyone in earshot understood what He was about to say...

The Truth
"I tell you the truth, anyone who sneaks over the wall of a sheepfold, rather than going through the gate, must surely be a thief and a robber! But the one who enters through the gate is the shepherd of the sheep.  The gatekeeper opens the gate for him, and the sheep recognize his voice and come to him.... I tell you the truth, I am the gate for the sheep.  All who came before me were thieves and robbers... Yes, I am the gate.  Those who come through me will be saved... the thief's purpose is to steal and kill and destroy but I came to give them a rich and satisfying life."(John 10:1-10 in part)

When Adam and Eve were banished from Eden, God stationed at the entryway, a mighty cherubim with a flaming sword to guard the Tree of Life.  Eternal life was no longer accessible to man.  But now Jesus has placed Himself at the gate, thus opening the way again.  Those who claim there is a way other than through Jesus, are warned in the passage in John 10 that they are mistaken.

The Thief
We often hear this verse applied to satan as the thief, and although the attribute fits, I think there is a more widespread implication.  Jesus said anyone who tries to circumvent the true way is a thief and a robber.

The Blind
Anyone pointing to another way in is doing the opposite of what Jesus does.  I believe He was making a judgment call on the Pharisees (who believed they were immune to condemnation by virtue of their positions) who were already scheming and planning His arrest.  This is what He meant in this exchange:

Some Pharisees who were standing nearby heard Him and asked, "Are you saying we're blind?" 
"If you were, you wouldn't be guilty," Jesus replied, "but you remain guilty because you claim you can see." (John 9:40-41 emphasis added)

The Truth
The gate is there for a purpose, to keep out those who seek to do harm to the ones inside the fold.  The sheep follow their shepherd to the place of safety and well-being, knowing instinctively his voice and his intentions toward them.  By laying down His life, Jesus is both The Good Shepherd and The Gate.