XIV. That we may validly infer the existence of God from necessary
existence being comprised in the concept we have of him.

When the mind afterwards reviews the different ideas that are in it,
it discovers what is by far the chief among them--that of a Being
omniscient, all-powerful, and absolutely perfect; and it observes
that in this idea there is contained not only possible and
contingent existence, as in the ideas of all other things which it
clearly perceives, but existence absolutely necessary and eternal.
And just as because, for example, the equality of its three angles
to two right angles is necessarily comprised in the idea of a
triangle, the mind is firmly persuaded that the three angles of a
triangle are equal to two right angles; so, from its perceiving
necessary and eternal existence to be comprised in the idea which it
has of an all-perfect Being, it ought manifestly to conclude that
this all-perfect Being exists.

XV. That necessary existence is not in the same way comprised in
the notions which we have of other things, but merely contingent
existence.

The mind will be still more certain of the truth of this conclusion,
if it consider that it has no idea of any other thing in which it
can discover that necessary existence is contained; for, from this
circumstance alone, it will discern that the idea of an all-perfect
Being has not been framed by itself, and that it does not represent
a chimera, but a true and immutable nature, which must exist since
it can only be conceived as necessarily existing.