Final answer:
Berkeley's immaterialist ontology led him to reject materialism and determinism on the grounds that they deny spiritual or intentional causation in our perceptions and actions, a stark contrast to his view that everything sensed or perceived is an effect of divine will.
Step-by-step explanation:
George Berkeley was distressed by materialism and determinism as they contradicted his immaterialist ontology where only spirits and ideas truly exist, and all physical sensations are derived from divine causation. Materialism's implication that inanimate matter can have causal powers and determinism's insinuation that human actions are predetermined without any spiritual or intentional influence were antithetical to Berkeley's idealist philosophy. He believed that material objects do not exist independently of perception and that our sensory experiences are ideas imparted by God's will, contrary to materialism which denotes a reality independent of mental perceptions and determinism which negates spiritual or intentional causation in our actions.
Berkeley's idealism is rooted in the firm belief that physical objects cannot exist outside of perception, as sensations are dependent on spiritual causation. He argued against the materialist worldview, which denies the role of psychical functions like sensing and thinking in the most pervasive processes of nature. Additionally, Berkeley found determinism distressing, as it leaves no room for the intentional acts powered by spirits, which he saw as essential for free will and the existence of the soul.