Leonardo of Pisa met the Hindu-Arabic numerals as a boy in Bugia, on the North African coast, where his father ran a trading post, and the Liber Abaci of 1202 is his attempt to make Latin Europe use them. It opens by introducing the nine figures and the sign for nothing, then spends most of its length on the arithmetic a merchant actually needs: converting between the currencies and weights of different cities, dividing profits in a partnership, calculating interest, alloying metals, testing whether an answer is right.
The resistance it met is easy to underestimate. Roman numerals were embedded in accounts, in law and in the reckoning board, and the new figures were held to be easy to alter, so several Italian cities forbade their use in official books for a long time afterwards. What carried them in the end was commercial arithmetic taught in the vernacular reckoning schools, not scholarly argument. The religious consequence is indirect and real. Calendar work, and above all the computation that fixes the date of Easter from the moon and the equinox, is arithmetic done at a scale that positional notation makes tractable and Roman numerals do not, and the same is true of the astronomical tables the calendar depends on.