D. W. Parry explains synthetic parallelism as follows:
Synthetic parallelism, as a rule, is composed of two lines, neither of which are synonymous or antithetical. Rather, in this form, line one presents a declaration and line two gives the explanation or adds some thing new or instructive to the first line. It is called synthetic because a synthesis, or coordination between the two elements takes place. First the idea or event of line one is introduced, then follows the realization, the completion, or finish of the thought. Ridderbos has identified synthetic parallelism as being a form, “in which the second line develops or completes the thought in a way that could not be determined from the first line. The parallelism is looser and the corresponding terms do not line up as neatly.”– Donald W. Parry – Poetic Parallelisms in the Book of Mormon
An example of synthetic parallelism in the Book of Moses is in chapter 1 verse 39:
For behold, this is my work and my glory—
to bring to pass the immortality and eternal life of man.
Why would Joseph Smith include different types of parallelism in the Book of Moses if it wouldn’t be noticed by anyone at the time?