On this view, it is not enough to say that God’s attributes, for example, are necessary to his being; rather, the multiplicity of attributes is only apparent. In reality, God is a being without any multiplicity at all, a simple being for whom any language suggesting complexity, distinctions, or multiplicity is entirely unsuited.
That is essentially the Plotinian neo-Platonic view, in which the best name of God is One. In the preceding section, I criticized Moltmann for equating this notion with monotheism. For Plotinus, even the name One is inadequate, since God is utterly beyond the descriptive power of human language. But One is the best we can do, since unity is prior to multiplicity and more noble than multiplicity.
Frame, John M.. Systematic Theology: An Introduction to Christian Belief (p. 430). P&R Publishing. Kindle Edition.