“In that day this song will be sung in the land of Judah: ‘We have a strong city; God will appoint salvation for walls and bulwarks.”
God will appoint salvation for us, because it is of the Lord, and it will stand. There is no hope for the enemy: he fights against God, rather than puny man. If our strength was in ourselves, then all boasting would be vain: Satan and sin would defeat us. The covenant keeping Christ, however, has already ratified the terms - paying for all transgressions and earning us the eternal inheritance [Heb 9:15]. This is not a start and stop salvation, but He will keep us to the end, carrying us to the finish line. He says, “Even to your old age, I am He, and even to gray hairs I will carry you! I have made, and I will bear; even I will carry, and will deliver you [Is 46:4].” Sin shall not have dominion. Only believe the promises, rejoice, and sing with God.
Yes, our falls are numerous and troublesome. Yes, we are shaken by doubt, despair, and unbelief. Yes, we may think that sin will swallow us, because temptations unconquered make the flesh get hungrier. Yet, we have a mighty God, and when we’re at the bottom, He’s still on top. When we doubt, He abides faithful. "If we are faithless, He remains faithful, for He cannot deny Himself [2 Tim 2:13]."
Chastisement proves His love, so with godly fear and reverence, cast your eyes upon Him. Look up, poor soul, look up. Do not look to self at all.
Let your humility grow, and pray for all of your graces to be holy graces. If it is kindness, then let it be holy. War and fight with your sins [Rom 8:13].
God is not saying that it will be easy: He is saying that He is strong, and our wall is salvation. Nothing will penetrate. They will beat on the wall and bloody themselves, but they will never take away what God deposited, and that good thing He started He will also finish.