Albert Barnes Commentary Isaiah 27:3

"I Jehovah am its keeper; I will water it every moment: lest any hurt it, I will keep it night and day." — Isaiah 27:3 (ASV)

I the Lord do keep it — There is understood here or implied an introduction; as ‘Yahweh said’ .

I will water it every moment — That is, constantly, as a vinedresser does his vineyard.