The teaching begins with a division of the divine unity into parts. Tawhid al-rububiyya is the acknowledgement that God alone creates and sustains, which Muhammad ibn Abd al-Wahhab held that almost everyone already grants. Tawhid al-uluhiyya is the direction of worship to God alone, and it is here that his preaching concentrated, on the argument that acknowledging a creator is not the same as worshipping only him. The third part, tawhid al-asma wa al-sifat, concerns the names and attributes and follows the Hanbali habit of affirming what the texts say without construing it.
Kitab al-Tawhid, his short and much reprinted book, is built almost entirely out of Quranic verses and hadith arranged under headings, with very little argument of his own between them. That form is the message: the claim is that the sources say this plainly and that nothing beyond them is needed.
What the preaching addressed itself against were practices he read as directing worship elsewhere. Seeking intercession at the tomb of a saint, vows made at a shrine, and appeals to a holy man to secure something from God were treated not as excessive piety but as the specific error the Quran condemns. The practical consequences followed directly: the levelling of grave structures, the removal of shrine cults, and a general suspicion of anything that puts an intermediary between a worshipper and God.