15 Next is related what happened in Egypt. “And He increased,” he says, “His people exceedingly, and made them stronger than their enemies”. Even the whole of this is briefly set forth, in order that the manner in which it took place may be afterwards related. For the people of God was not made stronger than their enemies the Egyptians, at the time when their male offspring were slain, or when they were worn out with making bricks; but when by His powerful hand, by the signs and portents of the Lord their God, they became objects of fear and of honour, until the opposition of the hardened king was overcome, and the Red Sea overwhelmed the persecutor with his army.
16. “And He turned their heart so, that they hated His people, and dealt untruly with His servants”. Is it to be in any wise understood or believed, that God turns man's heart to do sin?...For they were not good before they hated His people; but being malignant and ungodly, they were such as would readily envy their prosperous sojourners. And so, in that He multiplied His own people, this bountiful act turned the wicked to envy. For envy is the hatred of another's prosperity. In this sense, therefore, He turned their heart, so that through envy they hated His people, and dealt untruly with His servants. It was not then by making their hearts evil, but by doing good to His people, that He turned their hearts, that were evil of their own accord, to hatred. For He did not pervert a righteous heart, but turned one perverted of its own accord to the hatred of His people, while He was to make a good use of that evil; not by making them evil, but by lavishing blessings upon those, which the wicked might most readily envy.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)