In Sensus plenior, the number two refers to a dualism of heaven and earth. In this dualism both are good, unlike in other dualisms. When there are two things, they represent the dual nature of the thing. Two trees, since Christ is the tree, represent his dual nature as God and Man. The left is the side of the flesh as represented by the clean animal, the goat, and the spiritual nature is represented by the sheep on the right.
Two sins are one sin against God in heaven and on earth. Though the sin on earth appears to be against man, all sin is against God. When David confessed for Uriah's death, he said, "Against you alone have I sinned."
The King represents the earthly while the priest represents the heavenly. Judges and prophets are mixtures of heaven and earth.
Width and length are similar to east/west and north/south which are representations of eternity/time and heaven/earth.
Two rivers are water/the word , which is expressed on earth and in heaven, as grace and holiness.
Summarizing the two's in Zechariah we might say, "Thy will be done on earth as it is in heaven".
Since this dualism is foreign to modern interpreters, this example of how to apply it may be helpful. Jesus interprets Joshua:
Jos 24:14 Now therefore fear the LORD, and serve him in sincerity and in truth: and put away the gods which your fathers served on the other side of the flood, and in Egypt; and serve ye the LORD.
Joh 4:23 But the hour cometh, and now is, when the true worshippers shall worship the Father in spirit and in truth: for the Father seeketh such to worship him.
Joshua associates sincerity with truth, and Jesus associated the Spirit with truth. Since they are both associated with truth, they become a pair. The spirit is the heavenly reality, and sincerity is it's expression on earth.
We don't really understand the heavenly reality. But we get a glimpse of it when we understand sincerity in truth. Sincerity in truth is the earthly expression of the spiritual reality of worshiping in spirit and truth.
The duality, when identified, helps us understand spiritual realities by the example of the earthly expression of it.