Augustine of Hippo
Catena Aurea · Matthäusevangelium 6
Lay not up for yourselves treasures upon earth, where moth and rust doth corrupt, and where thieves break through and steal: But lay up for yourselves treasures in Heaven, where neither moth nor rust doth corrupt, and where thieves do not break through nor steal: For where your treasure is, there will your heart be also.
(Serm. in Mont. ii. 13.) For if any does a work with the mind of gaining thereby an earthly good, how will his heart be pure while it is thus walking on earth? For any thing that is mingled with an inferior nature is polluted therewith, though that inferior be in its kind pure. Thus gold is alloyed when mixed with pure silver; and in like manner our mind is defiled by lust of earthly things, though earth is in its own kind pure.