BBC: Genesis 7:2-5
Take with you seven pairs of all clean animals, the male and his mate, and a pair of the animals that are not clean, the male and his mate, and seven pairs of the birds of the heavens also, male and female, to keep their offspring alive on the face of all the earth. For in seven days I will send rain on the earth forty days and forty nights, and every living thing that I have made I will blot out from the face of the ground.” And Noah did all that the Lord had commanded him. – Genesis 7:2-5
This passage contains plentiful symbolism that is inherently practical to understanding future passages of Scripture. There are three pairs of clean animals as oppose to just one of the unclean. This shows God’s favor toward man after the destruction of the earth by providing him with animals for sacrifice. The final clean animal is for the covenant sacrifice that Noah will perform after the flood waters has subsided (Gen 8:20).
Also, the seven days are determined from the decree of God before the rains would come. In contrast to a day of rest (Gen 2:2), God is beginning a new creation at the culmination of these days. This “perfect” amount of time is followed by the complete and full amount of time required for purification. This will be seen again with the judgment of Israel in the wilderness, Christ’s temptation and the period of time between Christ’s ministry and the destruction of the temple.