Deuteronomy 4:20

Ver. 20. Iron furnace— The same phrase is used, 1Ki 8:51 and Jer 11:4 to express the most cruel servitude, wherein God suffered them to be tried, like metals in a furnace of iron. Moses, in the next verse, repeats again, though he had mentioned it twice before, that the Lord was angry with him; which not only shews how near it went to his heart, but, at the same time, admonished them, that if the principal head of their nation, and a person so peculiarly favoured by God, was debarred from so desirable a blessing for a single offence; what must they expect, if revolting from the religion of a God so jealous of his honour, and so fearful in power.