The answer is that assurance is rooted in our election. Second Peter 1:10 says, “Be all the more diligent to confirm your calling and election, for if you practice these qualities you will never fall.” Divine election is the foundation of God’s commitment to save me, and therefore that he will undertake to work in me by sanctifying grace what his electing grace has begun.
This is the meaning of the new covenant. Everyone who believes in Jesus is a secure beneficiary of the new covenant, because Jesus said in Luke 22:20, “This cup that is poured out for you is the new covenant in my blood.” That is, by my blood I secure the new covenant for all who are mine.
Piper, J. (2023). The Bedrock of Assurance
We need to remember, first, that impatience is a manifestation of pride. We are impatient because we want to “be like God” (Gen. 3:5), who alone gets everything done all the time. God speaks, and it always happens. Nothing frustrates His will; nothing limits His accomplishments. He always accomplishes everything that He wants to accomplish, and He always does so at the precise moment that He wants it to be done. We are impatient because we are not like that, and we so desperately want to be. And since pride really is “the great sin,” as C.S. Lewis has said, we ought not to tolerate it or to turn a blind eye to it in any of its manifestations.
Guy Richard, Impatience
… righteousness is precious to God and is, in fact, required — not as the ground of our justification (which is the righteousness of Christ only), but as an evidence of our being truly justified children of God. This is what Paul prays for, and we should pray for. He prays in Philippians 1:10–11 “that you may approve what is excellent, and so be pure and blameless for the day of Christ, filled with the fruit of righteousness that comes through Jesus Christ, to the glory and praise of God.”
John Piper, Dirty Rags No More