Jamieson, Fausset and Brown on Deuteronomy 4:30

30. in the latter days, if thou turn to the Lord thy God--either towards the destined close of their captivities, when they evinced a returning spirit of repentance and faith, or in the age of Messiah, which is commonly called "the latter days," and when the scattered tribes of Israel shall be converted to the Gospel of Christ. The occurrence of this auspicious event will be the most illustrious proof of the truth of the promise made in De 4:31.