Professor Tremper Longman notes that “the single most common characteristic of Hebrew poetry is repetition, usually called parallelism.” In its simplest form, parallelism is when two lines say the same thing with different words, though modern research proves that the second phrase always carries forward the thought from the first phrase. Generally, the second line tends to clarify or heighten the first line. This is abundant throughout the Psalms. An example of this is found in Psalm 21:1.
Psalm 21 is David’s song of deliverance. The first line celebrates the victory over God’s enemies. It reads: “O LORD, in Your strength the king will be glad (21:1a)” The second line heightens and parallels the same idea: “And in Your salvation how greatly he will rejoice! (21:1b).” There is great similarity in both lines. The first line speaks of strength, while the second line likens strength to salvation. Again, in the first line, the king will be glad, whereas the second line states that he will greatly rejoice. They are both similar ideas, though the second line carries the thought further by stating that the king was not simply glad, he rejoiced greatly in the salvation of the LORD.In short, as Longman summarizes, “A, what’s more B.”
Parallelism served as a learning tool to the Hebrews, who were mostly illiterate. Hence, parallelism helped express their deepest longings in simple language. This form of poetry can be seen in many ways. There are synonymous, antithetic, emblematic, synthetic, and other forms of parallelism. Two forms of parallelism most conspicuous in Psalm 42 and 43 are the emblematic and synonymous.
The emblematic form of parallelism employs a metaphor. The first line will indicate something literal (ex. I will go to the house of the Lord) and the second line will employ a metaphor (ex. God is my rock). Psalm 42:1 provides a simple illustration of emblematic parallelism. The text reads: “As the deer pants for the water brooks, So my soul pants for You, O God.” The first line of this verse presents a literal analogy. The summer season brings about excruciating heat for the animals. The deer is in no better condition than any other. When the deer is hunted by other animals or by humans, it strives with all its might to find refuge. The water brooks provide not only refreshment, but an escape. To reach the water brooks is a matter of survival. This literal analogy is followed by the second line. This second part employs a metaphor. In the same manner a deer seeks passionately for the water brooks for survival and refreshment, so too, our souls pant for God. The psalmist experiences the same longing as the deer. It is only in the presence of God that he finds refreshment and security.
Another form of parallelism present in Psalm 42 is synonymous parallelism. This occurs when two or more lines are expressing the same idea in different words. The refrain of this psalm (42:5;11; 53:5) provides an excellent example of synonymous parallelism. The psalmist writes: “Why are you so downcast, O my soul? Why so disturbed within me?” The psalmist laments over his distress with these questions. They are synonymous, though the psalmist expresses himself using different words. The psalmist is both downcast (first line) and disturbed (second line). His pain is so great that he waxes poetically. The indication is that the psalmist, under inspiration, is writing not only concerning his own pain, but also the pain of his people. His very being is disturbed and downcast. In the midst of this agony, the writer still hopes in God. He sees by faith, and not by sight.
 Tremper Longman III, How to Read the Psalms. (Downwer Grove: IVP, 1988). 93. Note that the “strength” spoken in the first part is carried further in the text to mean “salvation.”
 Longman 98.
 This quotation is taken from the NASB.
 John D. Currid, from Judges through Poets course. Audio Lecture 10B.
 Tremper Longman uses Psalm 2 as another example of synonymous parallelism, in How to Read the Psalms, 99. If synthetic parallelism is a valid form, then Psalm 43:1 may be an example. “Plead my cause against an ungodly nation; rescue me from deceitful and wicked man.” The pleading of the psalmist is a pleading to be rescued from the ungodly nation, which are composed of deceitful and wicked man. The second line completes or supplements the first.