The 'lords of the earth' are those who are doing their Will. It does not necessarily mean people with coronets and automobiles; there are plenty of such people who are the most sorrowful slaves in the world. The sole test of one's lordship is to know what one's true Will is, and to do it.
The Commentaries of AL: Being the Equinox Volume V, No. 1 (ed. Weiser Books, 1975)