Commentaire sur Chroniques 2 17:12

was becoming greater - Heb. וְגָדֵל. Scripture uses] a similar expression in reference to three people: Isaac, Samuel, and Jehoshaphat, but concerning Moses, David, and Mordecai, it says וְגָדוֹל. Concerning Isaac, Samuel, and Jehoshaphat, it says, וְגָדֵל because it is not proper to say וְגָדוֹל, great [in the context in which the word appears in the verse]. In regards to Samuel, it says, (I Sam. 2: 21): “And the lad Samuel grew up with the Lord.” God forbid that it should say, גָדוֹל עִם ה', he was great with the Lord. Here too, he [Jehoshaphat] became great to an unusual degree, גָדֵל עַד לְמָעְלָה. It is therefore improper to say וְגָדוֹל, great. The same applies to Isaac.

towers בִּירָנִיוֹת, derived from בִּירָה, huge towers for strength.

and store cities storage cities, to put in them wheat, wine and grain.