Charles H. Spurgeon on Psalms 89:29

His seed also will I make to endure for ever. David's seed lives on in the person of the Lord Jesus, and the seed of Jesus in the persons of believers. Saints are a race that neither death nor life can kill. Rome and its priests, with their inquisition and other infernal cruelties, have laboured to exterminate the covenant seed, but "vain is their rage, their efforts vain." As long as God lives, his people must live. And his throne, as the days of heaven. Jesus reigns on, and will reign till the skies shall fall, yea, and when the heavens shall pass away with a great noise, and the elements shall melt with fervent heat, his throne shall stand. What a blessed covenant is this! Some commentators talk of conditions, but we fail to see any; the promises are as absolute as they can possibly be, and if any conditions as to the conduct of the favoured individuals can be conceived, they are disposed of in the succeeding verses.