The Lord is speaking words of comfort to you that your warfare is accomplished and your sins are pardoned (Isaiah 40:2).
This does not mean that the enemy will not continue to attack you. The devil will fight against you, but he will not prevail because the Lord is with you.
Additionally, the Lord is reinforcing you like a fortified city and an iron pillar.
For behold, I have made you this day a fortified city and an iron pillar, and bronze walls against the whole land— against the kings of Judah, against its princes, against its priests, and against the people of the land. They will fight against you, but they shall not prevail against you. For I am with you,” says the Lord, “to deliver you.” (Jeremiah 1:18-19)
The endurance race
Your warfare is not against flesh and blood but against principalities, powers, rulers of darkness of this world and spiritual wickedness in high places (Ephesians 6:12).
Hence, your weapons for this war are not carnal but mighty through God to tear down strongholds and false teachings; and to destroy every proud obstacles that come against the knowledge of God and capturing your thoughts to ensure that they obey Christ (2 Corinthians 10:4-5).
Your walk with God is a daily affair. It is not a race that you can to accomplish in a day.
When you compete in a race, you want to win. Usually it is the fastest person who will win.
But in this race of life, you will win with endurance, not with speed nor strength.
I returned and saw under the sun that— The race is not to the swift, nor the battle to the strong, nor bread to the wise, nor riches to men of understanding, nor favor to men of skill; but time and chance happen to them all. (Proverbs 9:11NKJV)
Related post: Make a highway to God.
I pray that you will run this race with patience until you reach the finishing line.
May God bless you.