Bring forth the old because of the new - Rather, clear away the old before the new; that is, in order to make room for the latter. Compare the margin reference.

And ye shall eat old store,.... What is very old, corn of three years old, as Jarchi and Kimchi (m) interpret it; such plenty should they have that it would be so long consuming:
and bring forth the old because of the new; out of their barns and granaries, to make room for the new, which they should have great quantities of, and scarce know where to bestow them; and therefore should empty their treasures and garners of the old, and fill them with new; or they should bring them forth out of their barns into their houses, to make use of themselves, or into their markets to expose to sale, being under no temptation to withhold against a time of scarcity in order to make more of it, see Proverbs 11:26; now all these temporal blessings promised may be emblems of spiritual things, and might be so understood by such who were spiritually enlightened; as of the rain of divine grace, and the blessings of it, and of the doctrines of the Gospel, sometimes compared thereunto, Deuteronomy 32:2; and of great fruitfulness in grace and good works, and of internal peace in the minds of good men, and of their safety and security from spiritual enemies; of fulness of spiritual provisions, even of things new and old, and which are laid up for them, Song 7:13; thus promises of a spiritual nature more manifestly follow.
(m) Sepher Shorash. rad.

ye shall eat old store--Their stock of old corn would be still unexhausted and large when the next harvest brought a new supply.

Notwithstanding their numerous increase, they would suffer no want of food. "Ye shall eat that which has become old, and bring out old for new." Multiplicabo vos et multiplicabo simul annonam vestram, adeo ut illam prae multitudine et copia absumere non possitis, sed illam diutissime servare adeoque abjicere cogamini, novarum frugum suavitate et copia superveniente (C. a Lap.). הוציא vetustum triticum ex horreo et vinum ex cella promere (Calvin).

Bring forth - Or, cast out, throw them away as having no occasion to spend them, or give them to the poor, or even to your cattle, that you may make way for the new corn, which also is so plentiful, that of itself it will fill up your barns.