Where did the high priest get the coals he carried into the altar of incense on the Day of Atonement?
The high priest took the coals from off the brazen altar. On the Day of Atonement, he carried those coals into the inner altar of incense, where he burned incense rather than animal fat. The incense smoke filled the room, and Scripture connects it to the prayers of the saints and Christ's finished work.
Les explains that the altar of incense was a small wooden altar covered with pure gold and had a grate. Especially on the Day of Atonement, the high priest would take coals from off the brazen altar and carry them into this little altar inside. He did not burn animal fat or anything like that on it; he burned incense. The smoke of that incense would literally fill the little room and, as it were, obliterate the very presence of God even from the high priest. Les ties this to Christ's finished work and notes that Revelation identifies the sweet odor of the incense as the prayers of the saints.