Your iniquities. This is a new sentence, not a continuation of Isaiah 65:6, which should be closed by a full stop. It is an incomplete sentence, needing for its completion the repetition of the verb shillamti, "I will recompense."
Which have burned incense upon the mountains (see 2 Kings 17:11; Hosea 4:13; Ezekiel 6:13; and comp. Isaiah 57:7). And blasphemed me; rather, reproached me (see Isaiah 37:4, Isaiah 37:17, Isaiah 37:23, Isaiah 37:24).
Therefore will I measure their former work; rather, therefore will I, first of all, measure their work into their bosom. The expression, "first of all," prepares the way for the encouraging promises of Isaiah 65:8-10.