3 ideas
Mathematics is treated as a language whose rules are a grammar for talking precisely about size, order and shape, rather than a body of eternal truths discovered by pure reason. Seen this way, learning mathematics resembles learning a foreign language: the symbols are shorthand sentences, and difficulty comes from not knowing the grammar, not from lacking a special gift.
Mathematical techniques appeared when practical problems demanded them. Calendar-keeping for agriculture produced astronomy and geometry, navigation produced trigonometry, and commerce and gunnery pushed toward logarithms and calculus. Teaching each technique alongside the problem that created it makes it understandable to ordinary people, because the learner recovers the original motive instead of memorizing a result with no context.
Clumsy number systems such as Roman or Greek alphabetic numerals kept calculation in the hands of specialists who used the abacus. The Hindu-Arabic place-value system with a symbol for zero let anyone do arithmetic on paper. A better notation democratizes computation and makes later advances possible, so stagnation in mathematics can come from poor symbols rather than a shortage of intelligence.