This verse is what Allah (swt) swears for.

By (mankind) Allah (swt) means all people without any exclusion.

Allah (swt) swears by the the time (of the afternoon) to teach us that the general principle of the survival of nations and civilizations lies in three conditions, if they are available in a community, then it will flourish and develop, but if one of these conditions is missed , the community will fall in ignorance. These conditions are: A fixed creed, the righteous deeds and advising to truth and to patience.