2 Tim. 2:13 is sometimes used as an attempt to show support for that Jesus accepts us as we are even if we slip up and do not have faith in him since he is ”faithful”. This however is only wishful thinking. Here is the entire context and notice the CONDITIONS that we christians must adhere to 1) to be dead with him, 2) to be ready to suffer for him and 3) to not deny him.
2 Tim. 2:11 It is a faithful saying: For if we be dead with him, we shall also live with him:12 If we suffer, we shall also reign with him: if we deny him, he also will deny us:13 If we believe not, yet he abideth faithful: he cannot deny himself.
This goes together well with a few other verses which show some serious conditions:
Matteus 10:33 But whosoever shall deny me before men, him will I also deny before my Father which is in heaven.
Lukas 9:26 For whosoever shall be ashamed of me and of my words, of him shall the Son of man be ashamed, when he shall come in his own glory, and in his Father’s, and of the holy angels.
Matteus 6:15 But if ye forgive not men their trespasses, neither will your Father forgive your trespasses.
There are no other hints in 2 Tim. 2 that would indicate that God is faithful to the extent that he would save us regardless of our own unfaithfulness and no matter how we behave. The words about his faithfulness follow right after several IF:s (conditions) and the information that he WILL deny us if we deny him. What then is Jesus faithful about? He is faithful concerning all things that the Scripture write about him and concerning his own statements and promises. This includes the promises to reward the righteous and punish the unrighteous, and the promises don’t only concern the risk for reduced rewards in GOd’s kingdom but about the issue of heaven or hell. If we choose to live in unrighteousness, he will still accomplish all things he said he would precisely because he IS faithful to his own words. The verse in question does NOT say that even if we cease believing and/or live in sin, Jesus would still accept us anyway! There is obviously a risk for that true christians can lose their faith and/or start to live in unrighteousness or else these warnings would be in vain.
“He cannot deny himself”. For Jesus to not save us when we fall is not the same thing as denying himself. To be faithful to his words is to not deny himself, regardless of if it concerns promises of rewards or promises of punishments. To act against his own convictions or against his heart would be examples of denying himself. Jesus would never act against his own personality or be disobedient to his own Father who always makes fair judgments. Jesus is always faithful to his promises and warnings. If we deny him, he will deny us, and if we lose faith in him Jesus will still be true to his word and do all those things he said he would.
We can read more conditions in the same chapter, and we can read about two persons – Hymenaeus and Philetus – who had erred from the truth. This means they used to be in the truth but wandered away from it and lost it. They also had the ability to overthrow the faith of others, due to their unscriptural claims:
2 Tim. 2:15 Study to shew thyself approved unto God, a workman that needeth not to be ashamed, rightly dividing the word of truth.16 But shun profane and vain babblings: for they will increase unto more ungodliness.17 And their word will eat as doth a canker: of whom is Hymenaeus and Philetus;18 Who concerning the truth have erred, saying that the resurrection is past already; and overthrow the faith of some.
2 Tim. 2:21 If a man therefore purge HIMSELF from these, he shall be a vessel unto honour, sanctified, and meet for the master’s use, and prepared unto every good work.22 Flee also youthful lusts: but follow righteousness, faith, charity, peace, with them that call on the Lord out of a pure heart.23 But foolish and unlearned questions avoid, knowing that they do gender strifes.24 And the servant of the Lord must not strive; but be gentle unto all men, apt to teach, patient,25 In meekness instructing those that oppose themselves; if God peradventure will give them repentance to the acknowledging of the truth;26 And that they may recover themselves out of the snare of the devil, who are taken captive by him at his will.