Albert Barnes Commentary Deuteronomy 16:18-22

"Judges and officers shalt thou make thee in all thy gates, which Jehovah thy God giveth thee, according to thy tribes; and they shall judge the people with righteous judgment. Thou shalt not wrest justice: thou shalt not respect persons; neither shalt thou take a bribe; for a bribe doth blind the eyes of the wise, and pervert the words of the righteous. That which is altogether just shalt thou follow, that thou mayest live, and inherit the land which Jehovah thy God giveth thee. Thou shalt not plant thee an Asherah of any kind of tree beside the altar of Jehovah thy God, which thou shalt make thee. Neither shalt thou set thee up a pillar; which Jehovah thy God hateth." — Deuteronomy 16:18-22 (ASV)

These verses are closely connected in subject with the following chapter and introduce certain directions for the administration of justice and the conduct of the civil government of the people in Canaan. During the lifetime of Moses, he himself, especially inspired and guided by God, was sufficient for the duties in question, with the aid of the subordinate judges (compare Exodus 18:13 and following). But now that Moses was to be withdrawn, and the people would soon be scattered throughout the land of Canaan, regular and permanent provision must be made for civil and social order and good government.

Deuteronomy 16:21

A grove ... - Render: You shall not plant for yourself any tree as an idol: literally as an Asherah, that is, an image of Astarte or Ashtaroth, the Phoenician goddess (compare Deuteronomy 7:5 note, Deuteronomy 7:13 note). The word is rendered “grove” by the King James Version also in Deuteronomy 7:5; Deuteronomy 12:3; Exodus 34:13; and Judges 6:25, but this rendering cannot be maintained, for the word is connected with various verbs that are quite inapplicable to a grove. The wooden idol in question was the stem of a tree, stripped of its boughs, set upright in the ground, and rudely carved with emblems.