Joshua 3:5

And Joshua said unto the people
On the third day; and the thirtieth day of the mourning for Moses, Jarchi says, was the first of the three days, and that being the seventh day of the month, this must be the ninth, as it is most clear the morrow was the tenth:

sanctify yourselves;
in a ceremonial sense, by washing their bodies and their clothes, and abstaining from their wives; and in a moral sense, by acts of religion and devotion, by prayer and meditation, and the exercise of repentance and, good works: it may denote that sanctification is necessary to our passage over Jordan, or through death to the heavenly Canaan, for without holiness no man shall see the Lord:

for tomorrow the Lord will do wonders among you:
in their sight and presence, and for them, by dividing the waters of Jordan, that they might pass through it as on dry land; this, as Kimchi says, was the tenth of Nisan, as is plain from ( Joshua 4:19 ) .