John 10:1 Verily, verily, I say unto you, He that entereth not by the door into the sheepfold, but climbeth up some other way, the same is a thief and a robber.
I would have to say that the imagery of an open window is the best way to relate to today’s verse. The window does two things. It offers a view of what is within. It is available for access into the room if no one is watching that might stop you.
The view from the outside might tempt the outsider to enter in. Having a view does not make you a part of what is going on within. Having a desire to be part of the group within, does not give the outsider an invitation to become part of the group. Viewing the group does not give you experience in what it feels like to be part of the group.
An open window might seem like an invitation, but it is not. Some might think, hey, they are in, what does it matter? You know that being in a group does not make you part of a group. The fact that the group hasn’t pushed you away does not mean acceptance.
What makes you one of this group is having come in by the door.
John 10:7 & 9 Then said Jesus unto them again, Verily, verily, I say unto you, I am the door of the sheep. I am the door: by me if any man enter in, he shall be saved, and shall go in and out, and find pasture.
So what makes the one who enters by the window a thief? Consider this, love and grace are shared among the sheep. The fellowship of the sheep is reciprocating. The one without Jesus has not the love of the Father nor can he share grace. All he can do is take, take, take.
1 John 1:3 That which we have seen and heard declare we unto you, that ye also may have fellowship with us: and truly our fellowship is with the Father, and with his Son Jesus Christ.
No Jesus, no fellowship.