וַהֲכִינוֹתִ֥י אֶת־מַלְכוּת֖וֹ עַד־לְעוֹלָ֑ם אִם־יֶחֱזַ֗ק לַעֲשׂ֛וֹת מִצְוֺתַ֥י וּמִשְׁפָּטַ֖י כַּיּ֥וֹם הַזֶּֽה׃
And I will establish his kingdom for ever, if he be constant to do My commandments and Mine ordinances, as at this day.
Rashi
Be strong and of good courage in order that your kingdom endure as the Holy One, blessed be He, has promised you, (verse 7): “... and I shall prepare his kingdom to eternity if he strengthens himself to perform My commandments, etc.”