In Joshua Chapter 2, we see when the Israelite spies are being sent out into Jericho to scout and gather military intelligence for the planned invasion.
A woman named Rahab, possibly the Innkeeper of Jericho, hid the two spies from the King of Jericho which was trying to find them after being spotted by the citizens of Jericho, which were aware of a possible Israelite invasion poised to happen very soon.
Rahab knows the God of the Israelites as the real and TRUE God, and Jericho will soon fall. With this revelation, she makes a deal with the Israelites through the spies she is helping.
The deal was simple. Help them out of Jericho without getting caught, safely and does not tell anyone of the Israelite planned invasion, and when the city does fall, the Israel army will not harm her or her family, and treat them like their own.
The spies agree and instruct her to put a red cord of scarlet cloth on the window that she led the spies out of to escape the city. So that when the Israelite army overtakes the city, the soldiers will know to not enter that specific home and simply pass it by. --------- I believe the spies were inspired by this idea through the spirit of death which came and struck down the firstborn of Egypt when the Israelites were still enslaved there.
The spirit bypassed all the Israelite homes which were ordered to mark the doors with sheep blood. All homes which had the sheep blood on it, the spirit passed it by and did not enter the home. --------
Like the marketing of sheep blood which led the Israelites from destruction, or the cord of scarlet marked on the InnKeepers window in Jericho that saved her and her entire family from destruction, our mark is our trust and faith in Jesus Christ alone.
Our mark is not good works, or deeds. God's word has said ALL are guilty of sin, and fall short of the glory of God.
Our sin is leading to destruction, that will be the judge and creator of the universe which hates sin and has nothing to do with it.
Jesus Christ is our mark, of which God's destruction passes us by, and does not enter our eternity. Everyone with the mark of this salvation through Jesus Christ is saved from that wrath that is poised to come on the world.
Jesus paid our debt toward sin by living a sinless life, and dieing on the cross, then defeating the death which we deserved by resurrecting.
This saving faith in Christ is offered freely for everyone. Atheists, Agnostics, Muslims, Hindus, regardless of your religion, rebellion or things you have done in the passed.. it is offered to you through faith in Jesus Christ alone.
Its freely given, not because we deserved it, but because of grace from our creator out of love.
Thankfully, he has made a way for us, and we do not have to do anything to try and earn it, just accept it as a free gift from him.