Joshua 2:18

18. Thou shalt bind this line of scarlet thread in the window A small rope or cord composed of crimson threads. The English version conveys the idea that this cord was used in letting down the spies. But the Hebrew, Septuagint, and Vulgate make the window the antecedent of which, thus the window through which thou didst let us down. The scarlet cord was probably the token (Joshua 2:12) given to Rahab in proof of their oath. But the scarlet of the thread by which she and her house were to be saved, though a suggestive emblem of the blood of the atonement, (as advanced by St. Clement,) can hardly be considered, like the blood of the paschal lamb on the door post, an appointed type.

And thou shall bring thy father The persons to whom deliverance is pledged must be separated front the mass of the people and gathered within the house of Rahab, otherwise they must perish in the impending universal destruction. So must those who hope to escape the general doom of this sinful world be gathered into the house of God, the Church of Jesus Christ.