MIDRASH TEHILLIM
1.....(26.5)
This verse is to be read in light of what is taugh in a Mishna, on each of the first seven days of Sukkot men circled the Altar once, reciting: "Please, O LORD, save now!" (Tehillim 118:25).
And with what did they circled the Altar?
It is said: "And you shall take for yourselves on the first day, the fruit of the hadar tree, date palm fronds, a branch of a braided tree, and willows of the brook, and you shall rejoice before the Lord your God" (Vayikra - Leviticus 23:40)
I wash my hands in purity implied that the festive wreath must be got through purchase, not through robbery, for in a Mishna we are tought, A fastive wreath must be innocent of violence or robbery, lest the advocate turn accuser.