What is "theists"

Usage examples of "theists".

Nor would any of human race merit his favour, but a very few, the philosophical Theists, who entertain, or rather indeed endeavour to entertain, suitable notions of his Divine perfections: As the only persons entitled to his compassion and indulgence would be the philosophical Sceptics, a sect almost equally rare, who, from a natural diffidence of their own capacity, suspend, or endeavour to suspend, all judgement with regard to such sublime and such extraordinary subjects.

For them to be generally accepted, they must convince atheists and theists alike.

How is this compatible with that perfect immutability and simplicity which all true Theists ascribe to the Deity?