25. refuse not--through unbelief.
      him that speaketh--God in Christ. As the blood of sprinkling is represented as speaking to God for us, Heb 12:24; so here God is represented as speaking to us (Heb 1:1, 2). His word now is the prelude of the last "shaking" of all things (Heb 12:27). The same word which is heard in the Gospel from heaven, will shake heaven and earth (Heb 12:26).
      who refused him--Greek, "refusing as they did." Their seemingly submissive entreaty that the word should not be spoken to them by God any more (Heb 12:19), covered over refractory hearts, as their subsequent deeds showed (Heb 3:16).
      that spake--revealing with oracular warnings His divine will: so the Greek.
      if we turn away--Greek, "we who turn away." The word implies greater refractoriness than "refused," or "declined."
      him that speaketh from heaven--God, by His Son in the Gospel, speaking from His heavenly throne. Hence, in Christ's preaching frequent mention is made of "the kingdom of the heavens" (Greek, Mt 3:2). In the giving of the law God spake on earth (namely, Mount Sinai) by angels (Heb 2:2; compare Heb 1:2). In Ex 20:22, when God says, "I talked with you from heaven," this passage in Hebrews shows that not the highest heavens, but the visible heavens, the clouds and darkness, are meant, out of which God by angels proclaimed the law on Sinai.

JFB.