In the post-1708 Russian orthography (the Civil Script), unlike the Russian recension of Church Slavonic, the use of accents is not codified and is not obligate.
That said, some printers of the Synodal translation did follow the Church Slavonic rules and marked accents to resolve homonyms and homographs.
Church Slavonic used (with some exceptions) the grave accent (вария) on the last syllables of phonetic words, and the acute accent (оксия) otherwise. Phonetic words included clitics, so sometimes you can see the acute accent on what seems to be the last syllable of a printed word, like то́ же, то́ ли, спаси́ мя etc.
In Old Church Slavonic, ь, ъ and the final и denoted actual vowel sounds that were pronounced and formed syllables. Even though in the Russian recension of Church Slavonic ь, ъ are no longer forming syllables and й is not a vowel, they still count as vowels for the orthographic purposes.
It means that in the words like тáкъ, чѣ́мъ etc. the stress falls on what is technically considered a penultimate syllable, and, hence, the acute stress mark is used. This tradition has carried over to the Russian Bible texts as well, even though in Russian ь, ъ are completely silent and are not pronounced in any way whatsoever.
та́къ говоритъ Господь
To resolve the homography between та́къ ("thus") and такъ "so, and, that" (Рахиль сказала: такъ пусть онъ ляжетъ съ тобою эту ночь)
The stress is to distinguish oblique forms of Илíй (Eli) from oblique forms of Илiя (Elijah).
To distinguish from и́меннымъ ("named, particular")
Вспомните, что̀ Онъ сдѣлалъ съ Авраамомъ, чѣ́мъ искушалъ Исаака, что̀ было съ Iаковомъ въ Сирской Месопотаміи
To distinguish the meaning of "what" (as in "remember, what He did") from that of "that" (as in "remember that He did").
To distinguish the verb ("cast" in past singular) from the noun и́звергъ "cruel person", literally "outcast".