Albert Barnes Commentary Psalms 107:38

"He blesseth them also, so that they are multiplied greatly; And he suffereth not their cattle to decrease." — Psalms 107:38 (ASV)

He blesses them also - In the manner immediately specified.

So that they are multiplied greatly - This was regarded as one of the highest blessings which God could confer, and hence, it was so often promised by him to the patriarchs, as a proof of his favor, that their seed should be as the stars of heaven, and as the sand upon the sea-shore (Genesis 13:16; Genesis 22:17; Genesis 26:4; Genesis 32:12).

And suffers not their cattle to decrease - The keeping of herds of cattle was also an important point in husbandry, and hence, it was a blessing that they were made to increase, and that they were kept from the diseases to which cattle are subject.