The security of the believer as he abides in Christ.

John 15:4 through John 15:6 (NLT)
⁴Remain in me, and I will remain in you. For a branch cannot produce fruit if it is severed from the vine, and you cannot be fruitful apart from me.

⁵“Yes, I am the vine; you are the branches. Those who remain in me, and I in them, will produce much fruit. For apart from me you can do nothing. ⁶Anyone who parts from me is thrown away like a useless branch and withers. Such branches are gathered into a pile to be burned.

We have a tremendous promise from Jesus if we listen to His voice and follow Him.

John 10:27 through John 10:29 (NLT)
²⁷My sheep recognize my voice; I know them, and they follow me. ²⁸I give them eternal life, and they will never perish. No one will snatch them away from me, ²⁹for my Father has given them to me, and he is more powerful than anyone else. So no one can take them from me.