You can indicate that Isaiah wrote this. You can also translate it in an active form. Alternate translation: "as Isaiah the prophet wrote" (See: [[rc://en/ta/man/translate/figs-explicit]] and [[rc://en/ta/man/translate/figs-activepassive]])
These phrases mean basically the same thing and are metaphors that refer to Jesus and his death on the cross. It was as if the people stumbled over a stone because they were disgusted when they considered Jesus's death on the cross. (See: [[rc://en/ta/man/translate/figs-doublet]] and [[rc://en/ta/man/translate/figs-metaphor]])
Because the words "stone" and "rock" are a metaphors for a person, you may need to translate this as "believes in him." (See: [[rc://en/ta/man/translate/figs-metaphor]])