Tafsiran Yesaya 57:5: Rashi & Ibn Ezra

You who inflame yourselves among the terebinths Who stimulate themselves with semen under the אֵלִים, they are the terebinth and the oak.

הנחמים באלים The best of the various explanations of this phrase is that it refers to idolatry;⁴The noun אלים signifies here trees under which idols were worshipped. See Rashi and Targum ad locum. הנחמים Who are conceived, similar in form to הנצבים that stood (Gen. 45:1), is the Niphal of יחם to conceive; comp. בכלּ יַחֵם whensoever (the stronger cattle) did conceive (Gen. 30:41). This expression is the description of children of transgression (ver. 4); comp., And in sin did my mother conceive me (Ps. 51:7).

who slaughter the children for a sacrifice to the idols.

clefts Heb. סְעִפֵי, the clefts of the rocks. Comp. (Jud. 15:11) “to the cleft (סְעִיף) of the rock.”