Albert Barnes Commentary Psalms 18:43

"Thou hast delivered me from the strivings of the people; Thou hast made me the head of the nations: A people whom I have not known shall serve me." — Psalms 18:43 (ASV)

You have delivered me from the strivings of the people - From the contentions of the people, or from the efforts which they have made to overcome and subdue me. The allusion is to the efforts made by the people, under the guidance of their leaders. It is not strivings among his own followers, but the efforts, the strivings, the contentions of his enemies, who endeavored to obtain the mastery over him, and to subdue him.

You have made me the head of the heathen - The head of the nations; that is, the nations around. In other words, he had, by the divine aid, brought them into subjection to him, or so subdued them that they became tributary to him. The word heathen with us expresses an idea which is not necessarily connected with the original word. That word is simply nations - גוים gôyim. It is true that those nations were pagans in the present sense of the term, but that idea is not necessarily connected with the word. The meaning is that surrounding nations had been made subject to him, or that he had been made to rule over them.

David, in fact, thus brought the surrounding people under subjection to him and made them tributary. In 2 Samuel 8, he is said to have subdued Philistia, and Moab, and Syria, and Edom, in all of which countries he put garrisons, and all of which he made tributary to himself.

A people whom I have not known shall serve me - People whom I had not previously known. This is the language of confident faith that his kingdom would be still further extended, so as to embrace nations previously unknown to him. His past victories, and the fact that his kingdom had been so established and was already so extensive, justified the expectation that it would still be further enlarged, that the fame of his conquests would reach other nations, and that they would willingly yield to him. After the victories which he had achieved, as celebrated in this psalm, this might be expected to follow as a matter of course. It is the triumphant exultation of a conqueror, and it seems to have been his expectation, not that his successors would extend the empire, but that other nations would become voluntarily subject to him.