Charles H. Spurgeon on Psalms 78:1

To the words of my mouth. Was it not sufficient for the parallelism to say, To my words? Obviously. Why then is there any notice taken of the mouth? Because those who can prescribe laws to their subjects are also those who scorn to address them with their mouth. Such is the custom of kings, princes, pontiffs, both Roman and others. For the higher every one rises in dignity, the less he considers it becoming to him to speak to the people, to teach and instruct them by word of mouth. They think they owe nothing to the people, but are altogether taken up with this, that they may be looked up to as princes, and so retain a certain secular majesty of command. But, with one's own mouth to teach the ignorant, is a singular proof of love and paternal affection, such as becomes the preceptor, pastor and teacher. This Christ most constantly employed, because he was touched with paternal affection towards the lost sheep, and came as a shepherd to seek them. The manner of earthly princes he therefore rejected, and clothed himself with that paternal custom which becomes the shepherd and teacher, going about and opening his mouth in order to give instruction. See Matthew 5. Rightly, therefore, was the prophet not content with saying, Give ear, O my people, to my law: he adds, Incline your ears to the words of my mouth. Thus he indicates that he was about to address and instruct them with paternal affection. Musculus.