In theology, the doctrine of divine simplicity says that God is without parts
Personally, I have a hard time grasping this concept. Moreover, I couldn't find any scriptural support for this doctrine.
A better definition
When we speak of God’s simplicity then, in the most elementary sense, we are speaking of his not having parts, of his non-compositeness. “We use the term,” Berkhof explains, “to describe the state or quality of being simple, the condition of being free from division into parts, and therefore from compositeness” 1
Secularist would use the Ultimate Boeing 747 gambit to point out how a "simple" God was able to create a very complex universe.
I had a feeling that the doctrine of divine simplicity was born from logical necessity, just as the Euclideian geometry needs aussme that two parallel lines will not intersect.
Oh well, I'm like an ant who couldn't understand what Internet is.
I'm currently reading Euthyphro, God's Nature, and the Question of Divine Attributes, which discuss Divine Simplicity, and the philosophies used to describe how God is "simple".