In Luke 16:1-12 [1] And he said also unto his disciples, There was a certain rich man, which had a steward; and the same was accused unto him that he had wasted his goods. [2] And he called him, and said unto him, How is it that I hear this of thee? give an account of thy stewardship; for thou mayest be no longer steward. [3] Then the steward said within himself, What shall I do? for my lord taketh away from me the stewardship: I cannot dig; to beg I am ashamed. [4] I am resolved what to do, that, when I am put out of the stewardship, they may receive me into their houses. [5] So he called every one of his lord's debtors unto him, and said unto the first, How much owest thou unto my lord? [6] And he said, An hundred measures of oil. And he said unto him, Take thy bill, and sit down quickly, and write fifty. [7] Then said he to another, And how much owest thou? And he said, An hundred measures of wheat. And he said unto him, Take thy bill, and write fourscore. [8] And the lord commended the unjust steward, because he had done wisely: for the children of this world are in their generation wiser than the children of light. [9] And I say unto you, Make to yourselves friends of the mammon of unrighteousness; that, when ye fail, they may receive you into everlasting habitations. [10] He that is faithful in that which is least is faithful also in much: and he that is unjust in the least is unjust also in much. [11] If therefore ye have not been faithful in the unrighteous mammon, who will commit to your trust the true riches? [12] And if ye have not been faithful in that which is another man's, who shall give you that which is your own?
See All... I don't understand why the master praised the unjust steward for being a thief. Can you please explain.

This story of the unjust steward has caused a great deal of trouble for many.  One author stated that it was, “the most difficult of all the Lord’s parables”.  Another author stated that he “gave up the matter in despair, affirming a solution of them impossible.”  I will not claim that I have nailed down the interpretation of the passage perfectly, but I will say that there are some things here that when considered in light of the story make a whole lot more sense than some of the interpretations that have been set forth in other places.

First of all consider the audience of the lesson.  In Luke 15:1-2 [1] Then drew near unto him all the publicans and sinners for to hear him. [2] And the Pharisees and scribes murmured, saying, This man receiveth sinners, and eateth with them.
See All..., we are told that the Lord was speaking with publicans, sinners, Pharisees and scribes in His audience.  In Luke 16:14And the Pharisees also, who were covetous, heard all these things: and they derided him.
See All... we find that the Pharisees are within hearing distance of our Lord's teaching.  Yet we find the main audience of our Lord is found in Luke 16:1And he said also unto his disciples, There was a certain rich man, which had a steward; and the same was accused unto him that he had wasted his goods.
See All..., where the Bible says, "And he said also unto his disciples".  The Lord is directing this lesson to the disciples, yet He is very much aware that Pharisees are able to hear what He is saying.

Now to deal with the passage itself.  First we see the accusation of the steward.  We are not told who the accuser was, but we would certainly think that it was someone who was trusted by the rich man.  The accusation was that the steward had taken the goods of the rich man and had wasted them (Luke 16:1And he said also unto his disciples, There was a certain rich man, which had a steward; and the same was accused unto him that he had wasted his goods.
See All...).  When the rich man receives this news, he at once calls upon the steward to give an account of his stewardship.  By the wording emplored we would think that this original communication was not done face to face, but rather the rich man sent a message to the steward and asked for an account to be given because his stewardship was about to be up (Luke 16:2And he called him, and said unto him, How is it that I hear this of thee? give an account of thy stewardship; for thou mayest be no longer steward.
See All...).  Once the steward receives this message he begins at once to make plans for his future.  He determines that he cannot dig (work a job that requires physical labor) and to beg he was ashamed (beg for his job or beg by the side of the road for funds) (Luke 16:3Then the steward said within himself, What shall I do? for my lord taketh away from me the stewardship: I cannot dig; to beg I am ashamed.
See All...).  He then comes up with a master plan so that after he is kicked out of his current stewardship he will have somewhere to go (Luke 16:4I am resolved what to do, that, when I am put out of the stewardship, they may receive me into their houses.
See All...).  His plan begins, he calls in his lord's debtors and asks how much they owe his lord.  The first debtor says an hundred measures of oil and the steward says sit down quickly and write fifty, the second debtor says he owes an hundred measures of wheat and the steward said take thy bill and write fourscore (eighty)  (Luke 16:5-7 [5] So he called every one of his lord's debtors unto him, and said unto the first, How much owest thou unto my lord? [6] And he said, An hundred measures of oil. And he said unto him, Take thy bill, and sit down quickly, and write fifty. [7] Then said he to another, And how much owest thou? And he said, An hundred measures of wheat. And he said unto him, Take thy bill, and write fourscore.
See All...).  The lord of the steward found out about this and he commends the steward for his worldly wisdom.  By doing these things he had taken the time to think ahead and make sure that when he was removed from his current stewardship he would have plenty of places to go.  The lesson is that we are to think ahead and make plans for the future.  The Lord's instruction to "make to yourselves friends of the mammon of unrighteousness" is to be taken in the context of the story.  It would be like preaching a sermon on the potter and the clay and telling the believers to keep themselves on the wheel of the potter.  It only makes sense in light of the story.  The Lord was teaching His followers to make plans for the future.  The Pharisees needed to think ahead of their coming judgment and get right with God, the disciples needed to think ahead of rewards in heaven and make plans now to labor for Christ.

This is by no means the Lord instructing His people to be unrighteous or to do unrighteous works, but He desires that the children of light would be wiser than the children of this world.