That is a promise to Timothy, one of the faithful.dhk
Maybe your god, but not the One I serve, if we believe not, He abideth faithful 2 Tim 2:13
If we believe not, yet he abideth faithful[To His Own Promises]: he cannot deny himself.
Timothy had already believed in Christ, by faith.
He grew up in the faith.
If there were times in his life when he got discouraged as a believer sometimes does, and his faith faltered God would still remain faithful, as God did with Peter, when Peter denied him. That is a promise to believers.
That is not a promise to unbelievers; to those who have never believed.
If you have never put your faith in Christ you are not saved, and Christ has no obligation to be faithful to you. You are under his wrath and condemnation, and even now the wrath of God remains upon you.