Charles H. Spurgeon on Psalms 98:3

He hath remembered his mercy and his truth toward the house of Israel. To them Jesus came in the flesh, and to them was the gospel first preached; and though they counted themselves unworthy of eternal life, yet the covenant was not broken, for the true Israel were called into fellowship and still remain so. The mercy which endureth for ever, and the fidelity which cannot forget a promise, secure to the chosen seed the salvation long ago guaranteed by the covenant of grace. All the ends of the earth have seen the salvation of our God. Not to Abraham's seed alone after the flesh, but to the elect among all nations, has grace been given; therefore, let the whole church of God sing unto him a new song. It was no small blessing, or little miracle, that throughout all lands the gospel should be published in so short a time, with such singular success and such abiding results. Pentecost deserves a new song as well as the Passion and the Resurrection; let out hearts exult as we remember it. Our God, our own for ever blessed God, has been honoured by those who once bowed down before dumb idols; his salvation has not only been heard of but seen among all people, it has been experienced as well as explained; his Son is the actual Redeemer of a multitude out of all nations. In these three verses we are taught how to praise the Lord.