Albert Barnes Commentary Hebrews 12:25

"See that ye refuse not him that speaketh. For if they escaped not when they refused him that warned [them] on earth, much more [shall not] we [escape] who turn away from him that [warneth] from heaven:" — Hebrews 12:25 (ASV)

See that you refuse not. That is, do not reject or disregard.

Him that speaketh. This refers to him speaking in the gospel. Do not turn away from him who has addressed you in the new dispensation and called you to obey and serve him.

The meaning is that God had addressed them in the gospel as truly as he had addressed the Hebrews on Mount Sinai, and that disregarding his voice now was as much to be dreaded as it was then.

Indeed, he does not speak now amidst lightnings, thunders, and clouds, but he speaks by every message of mercy, by every invitation, and by every tender appeal. He spoke by his Son (Hebrews 1:2); he speaks by the Holy Spirit, and by all his calls and warnings in the gospel.

For if they escaped not. If those who heard God under the old dispensation, who refused to obey him, were cut off. (See the comments on Hebrews 10:28).

Who refused him that spoke on earth. That is, Moses. The contrast here is between Moses and the Son of God, the head of the Jewish and the head of the Christian dispensation. Moses was a mere man and spoke as such, though in the name of God. The Son of God was from above and spoke as an inhabitant of heaven.

Much more, etc. (See the comments on Hebrews 2:2, Hebrews 2:3, and Hebrews 9:28).

(The term "spoke" in this context means "uttered the divine oracles.")