Full Idea
Human nature belongs equally to all …and hence it is the duty of every man that each man value and treat the other as naturally his equal, or as equally a man.
Gist of Idea
We are all equal in human nature, and hence should treat others as equals
Source
Samuel Pufendorf (On the Duty of Man and Citizen [1673], I.07)
A Reaction
Being 'equally a man' is a mere tautology, and any other sense of 'equal' needs to specify the respect of the equality (which obviously is not height). I would guess that the equality is in their common human needs, like food, drink, shelter, security.
Book Reference
Pufendorf,Samuel: 'On the Duty of Man and Citizen' [CUP 1991], p.61