"That it was the voice of Christ that fell upon the ears of the people from the quaking mount, as the principles of God’s law were announced in such grandeur and power, is plainly stated by the writer of the book of Hebrews. Speaking of Jesus the mediator of the new covenant, and referring to the time when the law was proclaimed amid the thunder and flames of Sinai, he says: "Whose voice then shook the earth: but now he that promised, saying, Yet once more I shake not the earth only, but also heaven." Hebrews12:26.That this is spoken of Christ there can be no question.
Acting for the Father, in whatever in their united counsel they willed to do, so he spoke for the Father, in whatever they had occasion to proclaim. Equal in the authority by which law was enacted, they were equally concerned in its promulgation. Whatever God does, Christ does, because God does it through him; and whatever Christ does, God does, because Christ does it by him. And as in actions, so in words: God’s words are Christ’s words, because God speaks by him; and Christ’s words are God’s words, because Christ receives them from him. Thus Paul says: "God, who at sundry times and in divers manners spake in time past unto the fathers by the prophets, hath in these last days spoken unto us by his Son." Hebrews 1:1,2."
From Looking Unto Jesus by Uriah Smith