בְּכָל־הַדֶּ֗רֶךְ אֲשֶׁ֨ר צִוָּ֜ה יְהוָ֧ה אֱלֹהֵיכֶ֛ם אֶתְכֶ֖ם תֵּלֵ֑כוּ לְמַ֤עַן תִּֽחְיוּן֙ וְט֣וֹב לָכֶ֔ם וְהַאֲרַכְתֶּ֣ם יָמִ֔ים בָּאָ֖רֶץ אֲשֶׁ֥ר תִּֽירָשֽׁוּן׃
Lumakad kayo sa buong daan na iniutos sa inyo ng Walang-Hanggan na inyong Diyos, upang kayo ay mabuhay at mapabuti kayo, at humaba ang inyong mga araw sa lupaing inyong aangkinin.
Ibn Ezra
all of the path This metaphor explains the abovementioned “to the right or to the left” [: 29] and it denotes the instructions, the decrees, and the judgments — the ultimate purpose of which is that you will revere — i.e., you, your son, and your grandson. Thus, the ultimate purpose of all the commandments is sincere faith. Faith is the fulfillment of man, and it is for faith that man was created, as it is written in Ecclesiastes [Ecclesiastes 12: 13]. Faith will also assure long life — long life for the nation in the land of Israel, and long life for the individual in the World to Come.
Sforno
למען תחיו וטוב לכם, in order that you will live enduringly in a good and happy frame of mind.
Or HaChaim
בכל הדרך…למען תחיון, "all along the way …in order that you may live, etc." The meaning of תחיון וטוב לכם והארכתם means "long life on earth." The additional promise of וטוב לכם refers to the good which they will experience in the hereafter. The meaning of the word והארכתם ימים בארץ is that the Israelites will not ever be exiled from their land.