The verse means: “Show hospitality, even though the corresponding return of hospitality to you may seem improbable; nevertheless, be hospitable in faith.” Compare Luke 14:13-14; Hebrews 13:2. Some interpreters (not unreasonably) understand by “bread” the seed from the produce of which bread is made. Seed cast upon the fertile soil flooded by the early rains would be returned to the sower in autumn with large increase.
Related Commentaries of Ecclesiastes 11:1
Ecclesiastes 11:1
1 Cast thy bread upona the waters: for thou shalt find it after many days.