3 For six years you shall sow your field, and for six years you shall prune your vineyard and gather in its fruits,
4 but in the seventh year there shall be a Sabbath of solemn rest for the land, a Sabbath to the LORD. You shall not sow your field or prune your vineyard.
As a further reminder to Israel about the importance of rest and reflection on God's hand at work in creation, the people were commanded to rest even their land at certain times. Israel failed to do this for hundreds of years and as a result were removed by God into captivity in another nation to be slaves while the land received it's rest.
Once again, it is not so much a matter of treating the land right, but of treating God right. We are to make sure that we follow his commands, even when they seem unusual or silly to us, and we are to do so with an attitude of reverence and honour towards him.