Mammon refers to wealth that has been given to us by God. We serve mammon (Luke 16:13) when we are passionately attached to our wealth and hold back a part of it for ourselves. Wealth so held back is mammon of unrighteousness (Luke 16:9). The Lord's command to make to ourselves friends from the mammon of unrighteousness means to let go of that which we are jealously holding on to.
This is the lesson of the foregoing parable about the corrupt steward. Having been warned by the rich man, he quickly makes friends from those he had cheated previously and is rewarded by his master for his good deeds despite his previous errors.
The interpretations above are consistent with that presented by the 11th century Byzantine (Orthodox) cleric, Theophylact of Ohrid. Theophylact further observes:
We must make friends for ourselves by means of this mammon of
unrighteousness, which is the money and wealth the Lord has given us
to spend for the needs of our brothers and fellow-servants, but which
we have hoarded for ourselves. But, even though it is late, we
understand where we are headed, and that there will be nothing we can
do when that day comes. Then it will not be the time for labor, nor
will it be seemly to beg, for the virgins who beg are foolish [Matthew
What should we do? We should divide this wealth among our brethren,
so that when we fail here, that is when we depart from this life,
the poor will receive us into everlasting habitations [Luke 16:9].
The everlasting habitations have been reserved for the poor in Christ,
and these poor are able to welcome into their heavenly habitations
those who befriended them in this life by giving them that wealth
which should have been given them in the first place because it is the
Master's. These are those debtors of whom it is said, All day long
the righteous showeth merch, and lendeth [Psalm 36:26 LXX], and
again, He that showeth mercy to the poor lends to God [Psalm 19:17