These closing strains gather together once more the main points of the previous verses, his deliverance from domestic foes, and his conquests over external enemies. These are wholly God's work. True thankfulness delights to repeat its acknowledgments. God does not weary of giving, we should not weary of praising the Giver and His gifts. We renew our enjoyment of our long-past mercies by reiterating our thankfulness for them. They do not die as long as gratitude keeps their remembrance green.
But the Psalmist's experience impels him to a vow (verse 50). He will give thanks to God among the nations. God's mercies bind, and, if rightly felt, will joyfully impel, the receiver to spread His name as far as his voice can reach. Love is sometimes silent, but gratitude must speak. The most unmusical voice is tuned to melody by God's great blessings received and appreciated, and they need never want a theme who can tell what the Lord has done for their souls. 'Then shall... the tongue of the dumb sing.' A dumb Christian is a monstrosity. We are 'the secretaries of His praise,' and have been saved ourselves that we may declare His goodness.
Verse 51 has been supposed by some to be a liturgical addition, on the ground that, if David were the author, he would not be likely to name himself thus. But there does not seem to be anything unnatural in his mentioning himself by name in such a connection, and the reference to his dynasty, based as it is on Nathan's promise, is most fitting. The last thought about his mercies which the humble gratitude of the Psalmist utters is that they were not given to him for any good in himself, nor to be selfishly enjoyed, but that they were bestowed on him because of the place that he filled in the divine purposes, and belonged to 'his seed' as truly as to himself. So lowly had his prosperity made him. So truly had he sunk himself in his office, and in the great things that God meant to do through him and his house. We know better than David did what these were, and how the promise on which he rested his hopes of the duration of his house is fulfilled in his Son, whose kingdom is an everlasting kingdom, and who bears God's name to all the nations.