This is it, &c., in contrast with Leviticus 10:1. The positive opposed to the negative. Note the emphasis on "This". this and nothing else: this very thing. Disobedience here is vital; this is why "judgment must begin at the house of God": 1 Peter 4:17, yea "the time is come".
I will. Note this double "I will": and compare it with the "must" of John 4:24. Compare John 3:7; John 3:14. All worship which has not Christ for its object, the glory of Jehovah for its end, and the Holy Spirit for its power, will be rejected and judged.
held his peace: in solemn submission to God's judgment on his two sons, just struck dead so soon after their anointing, installation, and investiture. Compare Leviticus 8:13.