He hath stretched out a line - The line of devastation; marking what was to be pulled down and demolished.
Albert Barnes
Notes on the Whole Bible
A line - Compare Isaiah 34:11. The destruction is systematic and thorough.
Matthew Henry
Concise Bible Commentary
A sad representation is here made of the state of God's church, of Jacob and Israel; but the notice seems mostly to refer to the hand of the Lord in their calamities. Yet God is not an enemy to his people, when he is angry with them and corrects them. And gates and bars stand in no stead when God withdraws his protection. It is just with God to cast down those by judgments, who debase themselves by sin; and to deprive those of the benefit and comfort of sabbaths and ordinances, who have not duly valued nor observed them. What should they do with Bibles, who make no improvement of them? Those who misuse God's prophets, justly lose them. It becomes necessary, though painful, to turn the thoughts of the afflicted to the hand of God lifted up against them, and to their sins as the source of their miseries.
SDA Bible Commentary (limited)
Volume 1-7
8. Stretched out a line. That is, a measuring line. This expression is used in Zech. 1:16 in reference to the rebuilding of the Temple. In 2 Kings 21:13 and Isa. 34:11 it is used, as here, of judgment and destruction. The implication is that as the architect builds with precision, so also does God destroy.