"Seven" (sheva) and "complete/full" (sava) are spelled with the same Hebrew consonants. Seven communicates a sense of fullness or completeness. There are two words used to describe God's Sabbath rest on the seventh day of creation: shabbat (Gen. 2:2-3) and nuakh (Exod. 20:11). Shabbat means rest in the sense of stopping all work. Nuakh means rest in the sense of settling and taking up residence. When God completes his work and rests on the seventh day of creation, the authors are saying that God's glorious presence fills the Earth. But he also takes up residence in creation with humanity -- Heaven and Earth are truly united in this moment.