“If we are faithless, He remains faithful, for He cannot deny Himself,” meaning, “He is faithful to judge you.” (2 Tim 2: 11-13; also see Rom 3:3-8 which clarifies further).
This passage is often misunderstood. He is faithful or true to His character and His word to judge unbelief. This passage does not promise comfort for unbelief. He might deny you, but He won’t deny Himself, or His character. “Let God be true and every man a liar.”
This is true even of Paul. Note what Paul says just before this passage: “For this reason I ENDURE all things for the sake of those who are chosen, so that they also may obtain the salvation which is in Christ Jesus and with it eternal glory.” (2 Tim 2:10)
Next Paul states the “hymn” or credal statement. Let me quote it all. Note the word “ENDURE”:
It is a trustworthy statement:
For if we died with Him, we will also live with Him;
If we ENDURE, we will also reign with Him;
If we deny Him, He also will deny us;
If we are faithless, He remains faithful, for He cannot deny Himself.
Paul is teaching Timothy why he endures and how important endurance is. Failure to endure leaves Paul in judgment like everyone else, because God must be true to Himself and judge him. But on the positive side, Paul and Timothy will reign through an enduring faith.
God saves us eternally through our faith in the One who died for us and lives forever. But our faith must endure or it is not saving. That is the faith God causes through the gospel.
Persevere. Endure. Keep on until the end. We will reign with Him!