The Bread of Anxious Toil

Unless the Lord builds the house, those who build it labor in vain. Unless the Lord guards the city, the guard keeps watch in vain.
It is in vain that you rise up early and go late to rest, eating the bread of anxious toil; for he gives sleep to his beloved.
Ps. 127:1-2 

It is not his first point or lengthiest commentary on Psalm 127:1, but Calvin rightly identifies works righteousness as one of this verse's meanings:
Now, if our terrestrial condition depends. entirely upon the good pleasure of God, with what wings shall we fly up into heaven? When a house is planned, or a certain manner of life is chosen — yea, even when laws are enacted and justice
administered, all this is nothing else than to creep upon the earth; and yet the Holy Spirit declares, that all our endeavors in this way are fruitless and of no value. So much the less to be borne with, then, is the folly of those who strive to penetrate even into heaven by their own power.
The next verse continues this train of thought, but with a hopeful twist at the end. There are millions and millions of God's children whose lives consist only of earning their daily bread through hard physical labor, and who eat their bread only to gain enough strength for another day's work. The psalm doesn't condemn them, but invites them not to be anxious, for rest will come. Perhaps this psalm is also an invitation to the more affluent to think about those who are forced into vicious cycles of anxious toil, seeing them not as expendable labor, but as God's beloved.

As I turn to God this morning, I'm reminded of one of my favorite evening prayers...

O Lord, support us all the day long, until the shadows lengthen and the evening comes, and the busy world is hushed, and the fever of life is over, and our work is done. Then in thy mercy grant us a safe lodging, and a holy rest, and peace at the last. In the Christ's Name, who taught me to pray...