Augustine of Hippo
Catena Aurea · Lukasevangelium 11
And I say unto you, Ask, and it shall be given you; seek, and ye shall find; knock, and it shall be opened unto you. For every one that asketh receiveth; and he that seeketh findeth; and to him that knocketh it shall be opened. If a son shall ask bread of any of you that is a father, will he give him a stone? or if he ask a fish, will he for a fish give him a serpent? Or if he shall ask an egg, will he offer him a scorpion? If ye then, being evil, know how to give good gifts unto your children: how much more shall your heavenly Father give the Holy Spirit to them that ask him?
(de Quæst. Ev. lib. ii. qu. 22.) Or by the bread is meant charity, because we have a greater desire of it, and it is so necessary, that without it all other things are nothing, as the table without bread is mean. Opposed to which is hardness of heart, which he compared to a stone. But by the fish is signified the belief in invisible things, either from the waters of baptism, or because it is taken out of invisible places which the eye cannot reach. Because also faith, though tossed about by the waves of this world, is not destroyed, it is rightly compared to a fish, in opposition to which he has placed the serpent on account of the poison of deceit, which by evil persuasion had its first seed in the first man. Or, by the egg is understood hope. For the egg is the young not yet formed, but hoped for through cherishing, opposed to which he has placed the scorpion, whose poisoned sting is to be dreaded behind; as the contrary to hope is to look back, since the hope of the future reaches forward to those things which are before.