Matthew Poole and continuators on Psalms 127:3

3 Loe, children are an heritage of the LORD : and the fruit of the womb is his reward .

Which he mentions here, partly because they are the chief of all these blessings; and partly because all the forementioned toil and labour is in a great measure and most commonly undertaken for their sakes.

They come not from the power of nature and from a mans conversation with his wife, or with a multitude of wives or concubines, which Solomon had, but onely from Gods blessing, even as an inheritance is not the fruit of a mans own labour, but the gift of his father, or rather the gift of God both enabling and inclining his father to give it to him.

Not a reward of debt merited by good men, but a reward of grace, of which we read Rom. 4. 4. which God gives them graciously, as Iacob acknowledgeth of his children, Gen. 33. 5. And although God give children and other outward comforts to ungodly men in the way of common providence, yet he gives them onely to his people as favours and in the way of promise and covenant.

Marginal references: Deut. 28. 4.