"Then Nebuchadnezzar the king was astonished, and rose up in haste, and spake, and said unto his counselors, Did not we cast three men bound into the midst of the fire? They answered and said unto the king, True, O king. He answered and said, Lo, I see four men loose, walking in the midst of the fire, and they have no hurt; and the form of the fourth is like the Son of God."
"The fire that did not so much as singe their clothes burnt the cords wherewith they were bound, and set them at liberty; thus God's people have their hearts enlarged, through the grace of God, by those very troubles with which their enemies designed to straiten and hamper them. They had no hurt, made no complaint, felt no pain or uneasiness in the least; the flame did not scorch them; the smoke did not stifle them; they were alive and as well as ever in the midst of the flames. See how God of nature can, when he pleases, control the powers of nature, to make them serve his purposes. Now was fulfilled in the letter gracious promise (Isa. xliii. 2), When thou walkest through the fire thou shalt not be burnt, neither shall the flame kindle upon thee.... They were not striving to get out, finding themselves unhurt; but, leaving it to that God who preserved them in the fire to bring them out of it, they walked up and down in the midst of it unconcerned....There was a fourth seen with them in the fire.... Those that suffer for Christ have his gracious presence with them in their sufferings, even in the fiery furnace, even in the valley of the shadow of death, and therefore even there they need fear no evil. Hereby Christ showed that what is done against his people he takes as done against himself; whoever throws them into the furnace does, in effect, throw him in. I am Jesus, whom thou persecutest."
~ Matthew Henry