The writer of Psalm 127 stresses that, when man undertakes to do something, success depends on more than hard work and sweat. The unseen, all-important factor is that God must bless what he does. This is true with respect to both house-building (vv. 1-2) and family-building (vv. 3-5).
The instruction this psalm gives would have been very appropriate—and necessary—for the Jewish pilgrims traveling to Jerusalem in the days following the exile. The temple was being rebuilt at that time. The nation of Judah was also just getting back on its feet. A two-fold temptation confronted them: 1) To rely too much on their own strength and ability for success in these ventures; and 2) To become discouraged or depressed, thinking the assignment that lay ahead of them was too difficult to tackle. As they chanted this song they would have been reminded and encouraged by Jehovah's promise that the success of their undertakings didn't depend on their might and skill, but on Him, their almighty and all-merciful Lord.
The psalm applies to all endeavors—whether small or great—which we heaven-bound pilgrims undertake throughout the duration of our trek. Whether it be the planting of a tree in the ground or the planting of our children in the garden of the Lord; whether it be the construction of a house made of wood and stone or the building of God's heavenly kingdom through the preaching of the Gospel; whether it be a secular business enterprise or the spiritual enterprise of building a Christian home or family or marriage. "All depends on our possessing God's abundant grace and blessing."
Labors carried on in His name are never in vain! Knowing this, we may lay our worries aside.
— From the Lutheran Spokesman