Definition:

Faithful (adj.): Early 14c., “sincerely religious, devout, pious,” especially in reference to Christian practice; mid-14c., “loyal (to a lord, friend, spouse, etc.); true; honest, trustworthy,” from faith + -ful. From late 14c. in reference to a tale, a report, etc., “accurate, reliable, true to the facts.” The noun sense of “true believer, one who is full of faith” is from late 14c. (Church Latin used fideles in same sense).

Connection: Near Paul’s very last words/letters/encouragement to all who will attend, as he continued to live rather than just talk faith:

Remember Jesus Christ, risen from the dead, the offspring of David, as preached in my gospel, for which I am suffering, bound with chains as a criminal. But the word of God is not bound! Therefore I endure everything for the sake of the elect, that they also may obtain the salvation that is in Christ Jesus with eternal glory.

The saying is trustworthy, for:

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 (2 Timothy 2:8-13 ESV).

Encouragement: Faithfulness is all.