But if not, be it known unto thee, O king, that we will not serve thy gods, nor worship the golden image which thou hast set up.

Wesley's Notes

3:18 But if not - It was therefore all one to them, which way God would honour himself; they were resolved to suffer rather than sin, and leave the cause to God. Indeed if God be for us, we need not fear what man can do unto us. Let him do his worst. God will deliver us either from death, or in death.

Jamieson-Fausset-Brown Bible Commentary

18. But if not, &c.-connected with Da 3:18. "Whether our God deliver us, as He is able, or do not, we will not serve thy gods." Their service of God is not mercenary in its motive. Though He slay them, they will still trust in Him (Job 13:15). Their deliverance from sinful compliance was as great a miracle in the kingdom of grace, as that from the furnace was in the kingdom of nature. Their youth, and position as captives and friendless exiles, before the absolute world potentate and the horrid death awaiting them if they should persevere in their faith, all enhance the grace of God, which carried them through such an ordeal.

Matthew Henry's Concise Commentary

3:8-18 True devotion calms the spirit, quiets and softens it, but superstition and devotion to false gods inflame men's passions. The matter is put into a little compass, Turn, or burn. Proud men are still ready to say, as Nebuchadnezzar, Who is the Lord, that I should fear his power? Shadrach, Meshach, and Abednego did not hesitate whether they should comply or not. Life or death were not to be considered. Those that would avoid sin, must not parley with temptation when that to which we are allured or affrighted is manifestly evil. Stand not to pause about it, but say, as Christ did, Get thee behind me, Satan. They did not contrive an evasive answer, when a direct answer was expected. Those who make their duty their main care, need not be anxious or fearful concerning the event. The faithful servants of God find him able to control and overrule all the powers armed against them. Lord, if thou wilt, thou canst. If He be for us, we need not fear what man can do unto us. God will deliver us, either from death or in death. They must obey God rather than man; they must rather suffer than sin; and must not do evil that good may come. Therefore none of these things moved them. The saving them from sinful compliance, was as great a miracle in the kingdom of grace, as the saving them out of the fiery furnace was in the kingdom of nature. Fear of man and love of the world, especially want of faith, make men yield to temptation, while a firm persuasion of the truth will deliver them from denying Christ, or being ashamed of him. We are to be meek in our replies, but we must be decided that we will obey God rather than man.