In a recent combox I was asked about resources concerning the Simplicity of God. Here, for those who are interested, are two more items related to this subject.
The Oxford book of Selected Philosophical Writings of St. Thomas includes (passage 24, pp. 230-240 in the edition I have) a section from the Commentary on the Sentences, related to “How we Know One Simple God by Many Concepts.” I couldn’t find this online, but the Oxford book says it’s taken from Book I of the Commentary, Distinction 2, 1.3. I thought it was helpful.
Similarly, there is another passage from the Commentary that I did find online: Book I, Distinction 8, Question 4, Concerning God’s Simplicity.
I hope that these will prove useful.