The 1920 LDS edition changed the number agreement here in Mormon 9:36 so that the be verb would agree with the subject these things rather than the singular nouns in the nearer parenthetical phrase (“yea even their restoration to the knowledge of Christ”). Subject-verb agreement in the original text was often based on proximity; for a list of examples, see under subject-verb agreement in volume 3. For each of these cases, the critical text will restore the original verb number, thus is here in Mormon 9:36.
Summary: Restore the nonstandard use of is in Mormon 9:36 (“these things … is according to the prayers of all the saints”); in the original text, subject-verb agreement was often determined by proximity rather than semantics.