I the Lord do keep it - There is understood here or implied an introduction; as ‘Yahweh said’ (compare Psalms 121:3-5).
I will water it every moment - That is, constantly, as a vinedresser does his vineyard.
Related Commentaries of Isaiah 27:3
Isaiah 27:3
3 I the LORD do keep it; I will water it every moment: lest any hurt it, I will keep it night and day.