John Calvin Commentary Psalms 128:4

"Behold, thus shall the man be blessed That feareth Jehovah." — Psalms 128:4 (ASV)

Lo! surely, thus blessed shall be the man who fears Jehovah. The Prophet here confirms the preceding teaching: that even in the outward circumstances of God’s servants during this temporary life, such evidence of divine favor and goodness is provided that it demonstrates our labor in serving Him is not in vain. Yet, since the reward of godliness does not always appear exceptionally prominent, he first uses the demonstrative particle, Lo! and then adds surely; for that is how I interpret the particle כי, ki.

However, we must always remember, as I have noted before, that the divine blessing is promised to us on earth in such a way that it does not completely occupy our thoughts and keep them groveling in the dust; for it is not fitting that our hope of the life to come should be stifled. This is why we do not always equally enjoy God’s benefits.