This is true, but it shows that whatever comes into being must have something beginningless that brings it into being. Thus, the existence of something beginningless necessarily follows. On their view, however, this does not establish the existence of the Necessary Existent except through that division, since they allow that what is beginningless may be contingent.
If they say, “If what is beginningless is contingent, it must have a necessary existent,” they cannot establish a necessary existent without establishing this contingent existent. Yet this is impossible and also entails circular reasoning: they cannot establish the Necessary Existent without establishing a contingent existent, nor can they establish a contingent existent without establishing that what comes into being is contingent and has an agent. But this entails only the existence of something beginningless, and on their view, what is beginningless need not be necessary in existence. Thus, they cannot establish the Necessary Existent until they establish a contingent existent that may be beginningless. This, however, cannot be established except by establishing a contingent existent that comes into being, which indicates only the existence of something beginningless. On their view, being beginningless does not entail being necessary in existence.
Furthermore, even if they establish the Necessary Existent, they have not established that He is distinct from these observable things except through the argument from composition, which is invalid.
Those who affirm indwelling can then say to them: “The Necessary Existent indwells.”
To clarify: they divided existence into necessary and contingent, but classified some contingent existents as beginningless and others as having come into being. Accordingly, the Necessary Existent cannot be established without establishing this contingent existent, yet this contingent existent cannot be established.
Moreover, they establish the contingent only by establishing what comes into being. Whatever comes into being must have something beginningless that brings it into being, but being beginningless does not entail being necessary in existence.