In Joshua, chapter two, verse twenty-one, the scarlet line is a cord that parallels the Passover lamb. The blood on the houses of the Israelites was to protect them from the judgment of God. The scarlet line on Rahab’s home brought safety and deliverance to her household. The conditions negotiated between Rahab and the spies had to be intact.
She agrees that if the conditions required were not performed, they would quit their oath, but if they were, she expected to receive fulfillment.
Immediately, in the sight of the spies, they might see that she conformed to their direction and might take notice where she fastened it. However, she might, at the sight of it, put in mind the design. For Rahab, it would be encouraging her faith in the safety of her and her father’s house.
The “Scarlet line or cord” was spun of threads dyed with cochineal, a deep and bright scarlet color. The color of the cord would distinguish Rahab’s house from other places. Partly, the spies might see it hung out before their departure, so they better know it at some distance. Partially, lest some accident might occasion a mistake or neglect about it: and partly, for her comfort, it is pleasant and encouraging to have her eye on the pledge of her deliverance.
Rahab bound the scarlet line in the window: probably soon after the departure of the spies. It was not formed, as some suppose, into the network, as a lattice, but to hang down the wall. Its red color made it conspicuous, and it was a sign and pledge of safety to Rahab’s house, as the bloody mark on the lintels of the Israelites’ houses in Egypt to that people. Rahab’s commitment to cooperating with the spies gave her favor from God.