Because thou ... - Because the kingdom of Israel or Samaria had done it.
The God of thy salvation - The God in whom alone was salvation; or who alone could protect thee (compare Micah 7:7; Hosea 2:15).
The rock of thy strength - God. A rock of strength is a strongly fortified place; or a rock which an enemy could not successfully assail. High rocks were selected as a place of refuge from an invading foe (see the notes at Isaiah 1:10, Isaiah 1:21). In allusion to this, God is often called “a Rock,” and a strong tower Deuteronomy 32:4, Deuteronomy 32:15, Deuteronomy 32:18, Deuteronomy 32:30-31, Deuteronomy 32:37; 1Sa 2:2; 2 Samuel 22:2-3, 2 Samuel 22:32; Psalms 18:31, Psalms 18:46; Psalms 19:14; Psalms 28:1; Psalms 30:1-2.
Shalt thou plant pleasant plants - Plants that are suited to produce pleasure or delight; that is, you shall cultivate your fields, and set them out with choice vines and plants in hope of a future harvest, but you shall be disappointed.
And shall set it with strange slips - The word ‘slips’ means the “cuttings” of the vine that are set in the ground to grow; or the shoot or sucker that is taken off and “set out,” or put in the earth to take root and grow, as is often done by farmers and gardeners. The word ‘strange’ here means “foreign,” those which are procured from a distance, and which are, therefore, esteemed valuable; plants selected with care. This does not mean, as Lowth supposes, strange and idolatrous worship, and the vicious practices connected with it; but it means that, though they should be at great pains and expense in cultivating their land, yet the enemy would come in and make it desolate.