the saying is tustworthy for:

2Tim2.11-13 (ESV)
If we have 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 uses a hymn to emphasize his concept on glory which we find in the previous verse. I am not certain whether this is Paul's own hymn, or one that is borrowed. My guess would be to lean on the borrowed end as he says "the saying is trustworthy" as though Timothy probably would have heard this hymn before having read this letter. In any case, it is a means by which Paul re-emphasizes his previous thought.

The hymn begins with the idea of dying to ones self so as to be alive in Christ. This is a prevalent theme in the writings of the Apostle Paul specifically when he talks about baptism. Romans 6:3-4 "Or have you forgotten that when we were joined with Christ Jesus in baptism, we joined him in his death? For we died and were buried with Christ by baptism. And just as Christ was raised from the dead by the glorious power of the Father, now we also may live new lives."

I am sure that the next stanza comes after the first for the purpose of reminding Timothy, that that unity that comes through baptism, assumes the necessity of endurance in this new life. Paul just finished talking about his own endurance to Timothy, now he points Timothy back to endurance, reminding him, and us, that endurance is not purely for the sake of facing adversity for the sake of adversity, but instead for the enjoyment and fulfilment of the coming kingdom.

The next line seems to take the hymn from a celebratory song to almost some of a warning very reminiscent of Jesus words in Matthew 10:33 "But whoever denies me before men, I also will deny before my father who is in heaven" Paul wants to make clear to the readers the importance of this concept "if we deny him, he will deny us"

The transition though affirms the believer that yes there is a severity in denying Christ, but we must not live in fear about the times where we lack faith, or where God seems distant, or our journey seems strained. "if we are faithless, he remains faithful." "for he cannot deny himself" or as the NLT puts it "for he cannot deny who he is"

I am so grateful for this reminder that my God is a God who remains faithful, who cannot live against his character which is a character of Love. Yet still challenged by the truths of my unity with Christ, my endurance through the journey, and the importance of seeing that No one face the judgment that comes through denying Christ.