Charles H. Spurgeon on Psalms 128:1

That walketh in, his ways. God makes blessed those that walk in his ways, because he himself walks with them. This is said concerning David, and it is explained how that companionship blessed him, 2Sa 5:10: "And David went on, and grew great, and the Lord God of hosts was with him": where the "and" may be taken as the causal particle "because." That God does indeed join himself to those who walk in his ways as companion and leader we have in 2Ch 17:3-4: "And the Lord was with Jehoshaphat, because he walked in the first ways of his father David, and sought not unto Baalim; but sought to the Lord God of his father." —Thomas Le Blanc.