The 1953 RLDS edition here introduced an obvious typo, “for their cause”. Parallelism with the preceding main clause supports the original use of “for this cause”:
and for this intent we keep the law of Moses …
and for this cause it is sanctified unto us for righteousness
The critical text will retain the original this in both instances.
Summary: Maintain in Jacob 4:5 the use of this in “for this cause” (the earliest extant reading).