# to keep

"to obey"

# that your days may be prolonged

"that I may prolong your days" or "that I may cause you to live a long time". Long days are a metaphor for a long life. This can be translated similarly to "prolong your days" in Deuteronomy 4:26. There are many metaphors in this chapter. They describe the greatness of the Promised Land and the wholehearted worship that is completely dedicated to Yahweh.