Your iniquities, and the iniquities of your fathers together, saith the LORD, which have burned incense upon the mountains, and blasphemed me upon the hills: therefore will I measure their former work into their bosom.
The apostle Paul (an expositor we may depend upon) has given us the true sense of these verses, and told us what was the event they pointed at and were fulfilled in, namely, the calling in of the Gentiles and the rejection of the Jews, by the preaching of the gospel, Rom 10:20, Rom 10:21.
Commenting on Isaiah 65:1-7
Your iniquities, and the iniquities of your fathers together (saith the Lord),.... That is, the punishment both of the one and of the other; these being alike, and continued from father to son, and approved of, and committed by one generation after another, till the measure was filled up; and then the recompence of reward is given for all of them together at once: which...
Their sin had been accumulating from age to age until God at last repaid it in full. mountains-- (Isa 57:7; Eze 18:6; Eze 20:27-28; Hos 4:13). their--"Your" had preceded. From speaking to, He speaks of them; this implies growing alienation from them and greater distance. work--the full recompense of their work (so Isa 49:4).