Ye have seen, i.e. heard, as Exo_20:18. He may use the word seen here, to intimate that this was all they could see of God, to wit, his voice and speech, and that they saw no image of him, as is expressed in a parallel place, and therefore should make no resemblances of him, as it here follows.
From heaven, i.e. from the lower heaven, to wit, the air, or the clouds, which were over the top of mount Sinai, Deu_4:36Neh_9:13; and so the word heaven is oft understood, as Gen_1:20Job_35:11Psa_79:2. And so this place may be reconciled with Heb_12:25, where this is said to be spoken upon earth.