The spies gave them the sign, that is, a scarlet cord which was to be tied in the window of the house.
This sign is not for Rahab only but also for Joshua to see and save.
And according to the covenant of the blood, she tied it in the window, and Joshua spared her.
When Jesus came he said all scriptures (Moses) speak of him and his gospel (or good news) of salvation, as is visible in the patterns of the salvation through faith in the gospel:
- Joshua son of Nun: Jesus Christ, the son born of virgin Mary
- Jericho: this world where the ruler of this world/air reigns holding a tight grip on its inhabitants
- Rahab (and her family who shared faith with her): a sinner who repented and through faith in the Lord got saved
- Scarlet chord tied in the window: the blood of Jesus
- Oath/Vow/covenant made in blood ("their blood, i.e., the blood of the believer in the house) will be on our head" v. 19): this is the blood of the new covenant Luke 22:20
(Note: Jewish tradition says Rahab was 10 when the Israelite came out of Egypt, so that while running the house of brothel she might have heard the chronology of the work the Lord had done during the forty years of their journey to the Promised Land, affirming the truth of The Apostle Paul saying faith comes through hearing the message. Romans 10:17
Hymn song to sing: Beneath the cross of Jesus
Beneath the cross of Jesus
I fain would take my stand,-
the shadow of a mighty rock
within a weary land;
a home within a wilderness,
a rest upon the way,
from the burning of the noontide heat
and the burden of the day.
O safe and happy shelter!
O refuge tried and sweet!
O trysting-place where heaven's love
and heaven's justice meet!
As to the holy patriarch
that wondrous dream was given,
so seems my Savior's cross to me
a ladder up to heaven.
There lies beneath its shadow,
but on the farther side,
the darkness of an awful grave
that gapes both deep and wide;
and there between us stands the cross,
two arms outstretched to save,
like a watchman set to guard the way
from that eternal grave.
Upon that cross of Jesus,
mine eye at times can see
the very dying form of One,
who suffered there for me:
and from my smitten heart, with tears,
two wonders I confess,-
the wonder of his glorious love,
and my own worthlessness.
I take, O cross, thy shadow
for my abiding-place;
I ask no other sunshine than
the sunshine of his face,
content to let the world go by,
to know no gain nor loss,-
my sinful self my only shame,
my glory all the cross.
Imagine it is Rahab (or you) signing the hymn meaning what the lyric says.
Useful link, click here for "a slim scarlet cord of redemption dangling in a window.