I and My Father are one. Eternal security is the biblical doctrine that once one comes to faith in Christ he is secure forever. Once saved, always saved is the way some put it. In the verses before us Jesus affirms that He gives eternal life to His sheep. That His sheep will never perish.
Eternal life is eternal.
All of this is comforting. There Jesus says that His sheep follow Him. He let no one think that he could presume to be a Christian while at the same time disregarding or disobeying His teachings. If we are not listening to Christ and are not following Him in faithful obedience, we are not His. The ones who follow.