Perseverance of the Saints?

2 Timothy 2:13 (KJV)
If we believe not, yet he abideth faithful: he cannot deny himself.

Aha! There we have it! Proof for the perseverance of the saints, one of the pillars of Calvinism.
But then again, just one verse up, Paul wrote "... If we deny him, he will also deny us"!
So what's going on?
The fact of the matter is that throughout the chapter, and indeed the entire epistle, is Paul reminding Timothy of his responsibilities.
He was to commit the doctrine to faithful men (v. 2), endure hardness and strive for masteries as a soldier of Christ (v. 3,5), labour as a husbandman (v. 6), endure all things for the elect's sakes (v. 10), put in remembrance the word of God (v. 14), be deligent to show himself approved of God (v. 15), shun profane and vain babblings (v. 16), flee youthful lusts (v. 22), avoid foolish and unlearned questions (v. 23), be gentle to all men and instruct in meekness (v. 24,25). Truly, we are created in Christ Jesus to work (c.f. Eph 2:10)! And if we do not, we can and will be rejected!

What Paul is saying here is echoed in Romans 3:3 (KJV)
"For what if some did not believe? shall their unbelief make the faith of God without effect?"
Unlike Greek mythology (and for that matter, even that of the Chinese!), the God of the bible does not "draw strength" from his devotees!
His existence, His Power, His Promise is not dependent on our beliefs! Unbelief in God, will be like the proverbial ostrich that buries his head in the sand.
At the end of the day, whether one be an atheist, skeptic, idolater or fallen away believer, one will finally have to acknowledge God, has to answer to God (c.f. Rom 2:16; 2Ti 4:1; Phi 2:10,11).
Wherefore, let us not be caught up in unbelief but be fervent to abide in Him, to fight the good fight, to finish the course, to keep the faith, that we may finally lay hold onto the crown of righteousness (2Ti 4:7,8)!