What's so particular about the first seven?
The first seven, China people's funeral custom, is based on the time of the deceased's death, plus the date and hour calculated by heavenly stems and earthly branches, but everyone used to think that "the first seven" refers to the seventh day after death.
It is generally believed that the soul of the deceased will go home in the first seven days. Family members should prepare a meal for the dead before their souls come back, and then they must avoid it. The best way is to sleep. If you can't sleep, you should hide under the bed. If the soul of the deceased sees his family, it will make him miss and affect his reincarnation.
It is also said that when you go home on the seventh day, your family should burn a ladder-like thing at home and let your soul follow this ladder to heaven.