Matthew Poole and continuators on Exodus 23:15

15 Thou shalt keep the feast of unleavened bread: thou shalt eat unleavened bread as I have commanded thee, in the time appointed of the month Abib: for in it thou camest out from Egypt: and none shall appear before me empty :

This may be either 1. a precept, as it is generally understood, that none should ever come at those times without some offering or other, for the support of the Levites and of the worship of God: but the determination of this or what they would give was left to their choice. Or 2. a promise to encourage them to come so oft from their remotest habitations to Ierusalem, because they should never appear before God in vain, i. e. to no purpose, or without some benefit, for so the word, rekam, oft signifies. So it may be parallel to Isa. 45. 19. I said not unto the seed of Iacob, seek ye me in vain: But the former sence is more probable by comparing this with its parallel place, Deut. 16. 16, 17.

Marginal references: chap. 13. 3. & 34. 18.; Deut. 16. 16. Eccl. 35. 4.