He sings that things are going to get better. Yes, but only when we get to heaven.
And God will wipe away every tear from their eyes; there shall be no more death, nor sorrow, nor crying. There shall be no more pain, for the former things have passed away. ~Revelation 21:4
Jesus said that in this world we will have tribulation.
These things I have spoken to you, that in Me you may have peace. In the world you will have tribulation; but be of good cheer, I have overcome the world. ~John 16:33
Jesus mentioned signs that His coming is near and He said that it will not be the end yet, but that it will only be the beginning of sorrows.
For nation will rise against nation, and kingdom against kingdom. And there will be famines, pestilences, and earthquakes in various places. All these are the beginning of sorrows. “Then they will deliver you up to tribulation and kill you, and you will be hated by all nations for My name’s sake. And then many will be offended, will betray one another, and will hate one another. Then many false prophets will rise up and deceive many. And because lawlessness will abound, the love of many will grow cold. But he who endures to the end shall be saved. ~Matthew 24:7-13
So yes, let us rejoice while singing that song, knowing that things will be better eventually. Glory be to God. Thank you Lord Jesus. Maranatha.