The Lord had Israel make holy garments for Aaron to wear when he functioned as the high priest, and after he would be gone, his sons wore those same clothes,
“And the holy garments of Aaron shall be his sons’ after him, to be anointed in them and to be consecrated in them” (Exodus 29.29).
These special men would put on these special garments to perform the special work of the high priest. Guess how many days he would wear them. As the next verse declares,
“Ex. 29.30 That son who becomes priest in his place shall put them on for seven days, when he enters the tabernacle of meeting to minister in the holy place” (Exodus 29.30).
When the Lord created the heavens and the earth, He created during the first six days, resting on the seventh.
When Israel began their freedom from Egypt, they observed the Feast of Unleavened Bread that lasted seven days.
Seven days shows not only a complete cycle, but the start of something new.