Wear simple and reasonably priced clothes, show an easy-going attitude and do not pursue luxury. And every seven days is a cycle, representing a kind of balance and law. This may imply that in our daily life, we need to maintain regularity and balance, and don't be overworked or overexcited. At the same time, seven is also a magical number, which has mysterious meanings in many cultures, such as seven deadly sins and seven virtues.
Generally speaking, this sentence expresses a simple, regular and balanced attitude towards life and psychological state.