In this passage the first instance of the prepositional phrase of myself belongs to the preceding verb say; that is, the text would read more naturally in English if the phrase of myself were shifted forward in the sentence: “behold now I do not say of myself that these things shall be”. But we frequently find in the Book of Mormon text instances where a prepositional phrase is displaced or delayed. For some examples, see under Mosiah 26:23; for an extensive list, see volume 3 under displaced prepositional phrases. Here in Helaman 7:29, the 1830 typesetter attempted to deal with this difficulty by placing commas around the phrase of myself. The critical text will, of course, maintain the original delayed placement of the prepositional phrase.
There are several examples in the text where of myself is delayed after a short phrase (such as a direct object, prepositional phrase, or adverbial) but not after a that-clause (except here in Helaman 7:29):
In an equal number of cases, of myself occurs right after the verb. In three cases, we have of myself followed by a that-clause:
In one case, of myself occurs before a long series of conjuncts involving the of preposition:
Here the of prepositional phrases following of myself act as the complement of the verb know: ‘I know of the spiritual … I know of God’. In all these other cases of longer complements, of myself precedes the complement. The only exception is here in Helaman 7:29.
Summary: Maintain in Helaman 7:29 the delayed placement of the prepositional phrase of myself after the that-clause (“behold now I do not say that these things shall be of myself”); in the standard text, commas around of myself are used to show that this prepositional phrase does not belong to the that-clause but to the preceding verb say.