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What did Spinoza mean by the attributes of thought and extension?

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Engraved portrait of Benedict de Spinoza by Friedrich Roth-Scholtz, showing Spinoza in formal 17th-century attire with a circular symbol in the upper left corner. — Benedict de Spinoza Benedict de Spinoza.

For Benedict de Spinoza, the attributes of thought and extension are the two ways through which human beings perceive the infinite essence of the one substance, which he identifies as God or Nature.12

Extension: This attribute represents the quality of having spatial dimensions. Spinoza viewed the physical world through this attribute, accepting mechanistic physics as the correct framework for understanding it.12
Thought: This attribute encompasses mental phenomena, which are explored through logic and psychology.12

Spinoza rejected the idea that mind and body are distinct entities that causally interact, a common problem in Cartesian philosophy. Instead, he proposed that they are not separate but are merely different aspects of the same events. Individual physical and mental entities are considered "modes" of the one substance: physical entities are modes of substance understood under the attribute of extension, while mental entities are modes of substance understood under the attribute of thought. Because God is the only substance, all such entities are ultimately modifications of God.12