'Seventh Day' in the Bible

In the eleventh year [after King Jehoiachin was taken to Babylon], in the first month, on the seventh of the month, the word of the Lord came to me, saying,

You shall do this on the seventh [day] of the month for everyone who goes astray [and sins through error or ignorance] and for him who is naive; so shall you make atonement for the temple (house).