To be faithful is to be trusted. It is to have the character and the commitment to do what one say they would do. Since God is truth, He also commits to finish what He said He will do. This is nowhere clearer than in the Triune God at work in history to bring about what he says.
- Jesus says “Don’t you know that I could ask my Father and He would immediately send twelve legions of angels? How then would Scripture be fulfilled if my mission happened some other way?” (Matt 26:53-54)
- Men decided not to bother breaking the bones of Jesus’ corpse so that Scripture would be fulfilled “Not one of His bones will be broken” without them knowing it (John 19:36)
The Father makes the plans (Eph 1:3-4), the Spirit is breathed out in conveying those plans (2 Peter 1:21), and the Word brings about exactly what the Triune God wanted to happen (Is 55:11). That means that when God makes promises, those commitments are from His very being: He follows through exactly as he commits to do! God is always unchangingly faithful.