The importance of digit 7 in islam

I am 21 year old don't have enough knowledge about Islamic things. But I am notice that the digit 7 has a special importance in Islam . like seven earth, seven sky, seven ocean, seven Continent, seven round during hajj and umra, seven destinations in Quran, seven days in week. A lot of others example in universe. Can people clear me the actual meaning of digit seven and the history of this digit with some other examples?