God is faithful (1Co 1:9): true to His word, keeping His promises, trustworthy, dependable; we can safely trust Him to do what He says He’s going to do.
We can see this both in Scripture (2Th 3:3) and in Nature: for every need He’s designed fulfillment. YHWH is good; we need Him to be faithful, and He is, more than we can know. (Je 17:7-8)
But the enemy lies to us about God’s nature, twisting God’s promises and promoting wrong expectations so when God doesn’t meet them we’re tempted to mistrust Him. Falling for his lies steals our joy and traps us in bitterness; it’s too painful.
So God set His bow in the clouds to remind us of His faithfulness (Ge 9:13); scientists still don’t fully understand how He does it. Jehovah’s gone out of His way to assure us that He’ll never break His Word; He makes no promise lightly; He puts His reputation on the line in every single one. God’s promises are exceedingly precious gifts, open doorways inviting us into His nature. (2Pe 1:4)
As we wait on the Lord, expecting Him to be faithful, we’re saved by hope; it’s an abundant life of faith rooted in the character and nature of God. (Jn 10:10)