A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments: Psalms: Psalms Chapter 127
A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown [1882]
suggest the view of the theme given.
so he giveth his beloved sleep--that is, His providential care gives sleep which no efforts of ours can otherwise procure, and this is a reason for trust as to other things (compare Mat 6:26-32).
Posterity is often represented as a blessing from God (Gen 30:2, Gen 30:18; Sa1 1:19-20). Children are represented as the defenders (arrows) of their parents in war, and in litigation.
adversaries in the gate--or place of public business (compare Job 5:4; Psa 69:12).