[Heb 1:3-4] The radiance of His glory here is referring to the mount of Transfiguration where Jesus shone forth light. Jesus upholds all things by the word of His power, which is a job attributed to Yahweh all throughout the Old Testament. Jesus’ purification for sins is effective and final, evidenced by his sitting down at the right hand of the majesty on high, inheriting a more excellent name than the angels.