Who is the “they” who will perish and how do I avoid being part of “they”? The verse is describing the world itself. The idea is if God created our world, it will not last forever. They will wear out like clothing (see Isaiah 50:9; 51:6,8)
Life as we know it will not go on forever, therefore we need to live for God because no matter what we accomplish for ourselves, in effect it has no meaning if this world as we know it will come to an end one day. This life is in effect “nothing” in comparison to eternity.
Why doesn’t God just “take us home” as soon as we realize that He exists and we should live for Him? The answer is that God gives us the honor and privilege of leading others to Him and helping others grow in Him. That too, is a good summary of the purpose of our lives as Christian believers.
 But Thou art the same, and Thy years shall have no end.
Although this may be obvious to those who trust in God, one day our lives will come to an end and even the sun we see will burn out one day. However, the God we believe in, does not age and will live forever. It is another reason to live for God and not just to live for our own pleasure.
 The children of thy servants shall continue, and their seed shall be established before Thee.
The good news about this Psalm is that it is “future oriented”. It not only sees life from God’s perspective, but it also sees our own future from God’s perspective. Our lives, as well as the lives of others who come after us, should also be set on living for God.
If we believe God exists and that eternal life is dependent upon that trust in Him, we should teach that to the next generation and as many people that are willing to listen.
We have observed from this chapter that we should live in such a way knowing that God rules over our world forever. We should not waste our lives just doing things for our own pleasure but remember that when we give our lives to Him and make time for Him, He then in turn gives us the desires of our hearts. Trust God to get you through the rough times of your life. He longs to help you.