Matthew Poole and continuators on Isaiah 57:5

5 Enflaming your selves with idols under every green tree slaying the children in the valleys under the clifts of the rocks ?

Heb. being enflamed, &c. lusting after them, and mad upon them, as the Phrase is, Ier. 50. 38. fervent both in making and in worshipping of them, as was observed, Isa. 44. 12, &c. It is a Metaphor borrowed from Whoredom to which Idolatry is oft compared.

Wheresoever you see an Idol erected, which was commonly done in Groves, or under great and shady trees, which both defended the Worshippers from the heat of the Sun, and were supposed to strike them with a kind of sacred Horrour and Reverence. See on Deut. 12. 2. 2. Kin. 16. 4. & 17. 10.

In way of Sacrifice to their Idols, after the manner of the barbarous Heathens; of which see on Lev. 18. 21. Deut. 12. 31. 2 Kin. 21. 6. & 23. 10.

Or, besides the brooks, which run in valleys: which was most commodious for such bloody work. He seems to allude to the valley of Hinnom in which these cruelties were practised, Ier. 7. 31. through which also the Brook Kidron is supposed to have run.

Which they chose either for shade, or for those dark vaults and hollow places, which were either by Nature or Art made in rocks, and which were convenient for, and frequently appointed to idolatrous uses.

Marginal references: Heb. with gods, or among the oaks.; 2 Kin. 16. 4.; Ezek. 16. 20. & 20. 26.