If it is true that...

Not all beings are contingent

Then it must be true that...

There is at least one necessary being

If it is true that...

There is at least one necessary being

and

Every necessary being either has its necessity caused by another, or has its necessity itself

and

There cannot be an infinite series of necessary beings each having its necessity caused by another

Then it must be true that...

There exists a necessary being having of itself its own necessity