Albert Barnes Commentary 1 Samuel 6:3

"And they said, If ye send away the ark of the God of Israel, send it not empty; but by all means return him a trespass-offering: then ye shall be healed, and it shall be known to you why his hand is not removed from you." — 1 Samuel 6:3 (ASV)

Send it not empty - See the marginal references. The pagan idea of appeasing the gods with gifts, and the scriptural idea of expressing penitence, allegiance, or love to God through gifts and offerings for His glory and for the comfort of our fellow worshipers, coincide in their practical result.