Deuteronomy 28:38

Thou shalt carry much seed out into the field, and shalt gather but little in; for the locust shall consume it.

Thou shalt carry much seed into the field yet gather little in because the locust consumes it stands as one of the curses that would follow Israel's disobedience. The sowing would be plentiful and the harvest scant, for locusts would eat the crop. God's promises to Israel were made upon condition of obedience, with blessings promised for obedience and curses threatened for disobedience. Disobedience brings loss in temporal things and a curse upon the land. Prosperity comes with obedience, and adversity is sent when the law is transgressed.

The loss of much-sown seed to locusts is a fearful result of transgression set in contrast with the blessings of obedience. The curse on vegetation grew heavier as the people continued to break God's commandments. The verse belongs to the directions in Deuteronomy 26, 27 and 28 that state plainly the blessings of obedience. Those directions express the principles of the law of God's kingdom made specific, so that minds are not left in ignorance and uncertainty.

They present the never-ceasing obligation of all whom God has blessed with life and health and temporal and spiritual advantages. The message has not grown weak with age, but God's claims are just as binding now and just as fresh in importance as His gifts are fresh and continual. The chapters to which the verse belongs are to be read carefully with Exodus 15 to show God's covenant of mercy. Diligently hearkening to His voice and doing right in His sight and keeping His commandments and statutes keeps away the diseases brought upon the Egyptians, because He is the Lord who heals.

Transgressing His law breaks down the barriers He erected to preserve His people in health and holiness, and brings disease and suffering of every kind. This was taught at Marah, where Christ leading Israel under the pillar of cloud put healing properties into the tree that sweetened the waters to show His power to cure the evils of the human heart. The conditional curse of sowing much but gathering little helps explain why the Lord refused to bring the adult army that left Egypt into the promised land.