Bible Notes Online - Psalms 127 - ESV
Commentary

A house built on God, as in Haggai, 1 Chr 28.10; Eccl 2.22-23.

v1: We must not presume upon God's blessing; rather we must depend on Him, and ask Him to bless, knowing that our labours are useless without Him. We are called to build, and to watch, but in His strength, and dependent on His blessing,

v2: "Vain," meaning a lie, or falsehood; used in Ezek 13.

v3-4: When God blesses there is fruit as well as growth. The shame of fruitlessness is gone; there is dignity in living in God's blessing.

v5: Blessing includes influence and authority, Deut 15.6.