One thing that long ago helped me to apprehend and appreciate the power of functional programming was to start thinking descriptively (in terms of facts and propositions) rather than prescriptively (in terms of imperatives and commands).

Thus, I read “(+ 1 2)“ as “the sum of 1 and 2” rather than ”add 1 and 2“. Similarly, I read ”(eq (+ 1 2) 3)“ as ”the difference between 3 and the sum of 1 and 2 is zero“.