“It is a sabbath of solemn rest to you, and you shall afflict yourselves. It is a statute for ever.”
This is repeated for emphasis. It is a sabbath of solemn rest in which they should afflict themselves in order to demonstrate penitence for sin and uncleanness. And this was a permanent statute ‘for ever', that is, into the distant future. In Israel there was the weekly sabbath which was the last day of a regular seven day period, what we call ‘a week', and special sabbaths for special occasions. This was a sabbath for a special occasion and could occur any day of the week.