Exodus 19:9-15

And the LORD said unto Moses, Lo, I come unto thee in a thick cloud, that the people may hear when I speak with thee, and believe thee for ever. And Moses told the words of the people unto the LORD.

Lo, I come ... in a thick cloud ... The deepest impressions are made on the mind through the medium of the senses; and so He who knew what was in man signalized His descent at the inauguration of the ancient church by all the sensible tokens of august Majesty that were fitted to produce the conviction that He is the great and terrible God. The whole multitude must have anticipated the event with feelings of intense solemnity and awe. The extraoradinary preparations enjoined, the ablutions and rigid abstinence they were required to observe, the barriers erected all round the base of the mount, and the stern penalties annexed to the breach of any of the conditions, all tended to create an earnest and solemn expectation, which increased as the appointed day drew near.

Verse 10-14. Sanctify them today and tomorrow, and let them wash their clothes. The whole people of Israel being about to be taken into covenant with God, and thereby constituted "a holy nation," were required to "wash their clothes" - emblematic of their ceremonial purity. It was a baptism-the sign of their admission to sacred privileges. 'When Yahweh admitted Israel to the rights of the covenant, He constituted them a "holy nation;" and all the children ever afterward born of those parents were, by their birth, holy in this respect, they were entitled to all the privileges of the covenant, when observed. For which reason succeeding generations of Israelites were never baptized, because they were already in the holiness, the passage to which such a baptism would signify' ('Johnstone, 'Israel after the Flesh,' p. 97).