Because the Lord is faithful and merciful

The Lord will perfect that which concerns me;
Your mercy, O Lord, endures forever. (Psalm 138:8, NKJV)

I really like how the NKJV translates verse 8. It brought me right back to the verse I mentioned yesterday.

I am sure of this, that he who started a good work in you will carry it on to completion until the day of Christ Jesus. (Philippians 1:6)

Why could David and Paul be so certain of this? Because of their own goodness and faithfulness?

No. It was because the Lord’s mercy, his steadfast love endures forever.

So let us sing with David,

I give you thanks, O Lord, with my whole heart;
before the gods I sing your praise;

I bow down toward your holy temple
and give thanks to your name for your steadfast love and your faithfulness. (1-2, ESV)