We were not meant to forget our mortality. The decisions we make every day should be in light of the fact that we will not live forever on this planet. I love Mute Math's song Progress. They say that "every moment in time is just an answer to find what you're here for, what you breathe for, what you wake for, what you bleed for." That's so true. If you get distracted, like I do almost every day, by the cares and comforts of this world, you'll forget that it's all going away someday. And if it's all going away someday, what's the point of life?
Thankfully, we don't have to despair. One of the benefits of Christ's death is that we would have purpose and meaning in this life. By repenting and trusting in His propitiatory sacrifice on the cross, we can be reconciled to God to receive freedom and abundant, everlasting life. And then, we don't have to fear death any longer because we have the favor of God on us.
Reflect on your mortality and live in light of eternity. I think that is what David is getting at in Psalm 39:4-6:
"O LORD, make me know my end and what is the measure of my days; let me know how fleeting I am! Behold, you have made my days a few handbreaths, and my lifetime is as nothing before you. Surely all mankind stands as a mere breath! Surely a man goes about as a shadow! Surely for nothing they are in turmoil; man heaps up wealth and does not know who will gather!"