Notes on the Bible, by Albert Barnes, [1834], at sacred-texts.com
This and the next two chapters contain enactments designed to protect human life, and to impress its sanctity on Israel.
In Deu 19:1-13 the directions respecting the preparation of the roads to the cities of refuge, the provision of additional cities in case of an extension of territory, and the intervention of the elders as representing the congregation, are unique to Deuteronomy and supplementary to the laws on the same subject given in the earlier books (compare the marginal reference).
The three cities of refuge for the district east of Jordan had been already named. Moses now directs that when the territory on the west of Jordan had been conquered, a like allotment of three other cities in it should be made. This was accordingly done; compare Jos 20:1 ff,
Thou shalt prepare thee a way - It was the duty of the Senate to repair the roads that led to the cities of refuge annually, and remove every obstruction. No hillock was left, no river over which there was not a bridge; and the road was at least 32 cubits broad. At cross-roads there were posts bearing the words Refuge, Refuge, to guide the fugitive in his flight. It seems as if in Isa 40:3 ff the imagery were borrowed from the preparation of the ways to the cities of refuge.
With the axe - literally, "with the iron." Note the employment of iron for tools, and compare Deu 3:11 note.
Provision is here made for the anticipated enlargement of the borders of Israel to the utmost limits promised by God, from the river of Egypt to the Euphrates (Gen 15:18, note; Exo 23:31, note). This promise, owing to the sins of the people, did not receive its fulfillment until after David had conquered the Philistines, Syrians, etc.; and this but a transient one, for many of the conquered peoples regained independence on the dissolution of Solomon's empire.
As a man's life is to be held sacred, so are his means of livelihood; and in this connection a prohibition is inserted against removing a neighbor's landmark: compare the marginal references.
Testify against him that which is wrong - Margin, more literally, "a falling away." The word is used Deu 13:5 to signify apostasy or revolt; here it is no doubt to be understood in the wider sense of any departure from the Law.
Both the men, between whom the controversy is - Not the accused and the false witness, but the plaintiff and defendant (compare Exo 23:1) who were summoned before the supreme court held, as provided in Deut. 17, at the sanctuary. The judges acted as God's representative; to lie to them was to lie to Him.
See the marginal references.