Read Psalms 127:1&2  There are 3 stories here in our 2 verses, but all 3 of them talk about the same thing.  The first story says that unless God builds the house, it is a waste of our time to try to build it ourselves.  We can work hard, but it is actually God who builds our spiritual house. The second story says that even though there is a watchman who is looking out over the city wall watching for the enemy to come, God is actually the one who protects the city from the enemy.  The third story is about us staying up all night worrying about what might happen tomorrow.  If God is powerful, and if God never sleeps, and if God is watching over us, we might as well just go to sleep and let God keep us safe.  After all, He can do a much better job of taking care of us than we can!