Something struck me while working for the Billy Graham Evangelistic Association - Billy Graham was said to have stated "most of life is filled with valleys." When you think of it, it's true. Scripture tells us that as believers we are to be people who "long for heaven." (see 2 Timothy 4:8). How can we long for heaven if we are always happy and comfortable in this world?
Another passage of Scripture elaborates exactly how I feel some days: "Now we know that if the earthly tent we live in is destroyed, we have a building from God, an eternal house in heaven, not built by human hands. Meanwhile we groan, longing to be clothed with our heavenly dwelling, because when we are clothed, we will not be found naked. For while we are in this tent, we groan and are burdened, because we do not wish to be unclothed but to be clothed with our heavenly dwelling, so that what is mortal may be swallowed up by life. Now it is God who has made us for this very purpose and has given us the Spirit as a deposit, guaranteeing what is to come. (2 Corinthians 5:1-5).
There's so many reasons I long for heaven. I'm a very optimistic person and the majority of my life I'm happy, but all of us face divers valleys that look strikingly similar to the "shadow of death" (Psalm 23) at many times in our lives. We will never find what makes us truly happy in this life or while in this "body of death." (Romans 7:24).
Numerous Scriptures concrete the fact that we are "aliens and strangers" on this earth (see 1 Chronicles 29:15, Hebrews 11:13, 1 Peter 2:11, John 17:14-16, 1 John 2:15, Psalm 119:19, etc.).
This world is not our home, we are just passing through.