Upon first glance, the content of Luke 16 seems a bit oddly disconnected. There are two parables, one brief explanation of only one of them, and a seemingly random and extremely brief teaching about marriage. But, looking more closely, we see the connections not only within the chapter, but to what has come before, and especially the parable of the Prodigal Father that immediately precedes this.
This has some easier-to-find understanding and some more difficult material. Jesus, though speaking to His disciples, is still speaking against the attitudes of the Pharisees (we find out in 16:14 that they're "peeking in" to this parable). The "bottom line" is perhaps clear and straightforward, and that is where Jesus ends up in verse 13. God and money are two different masters, and people will inevitably end up favouring one over the other. Trying to have it both ways simply will not work.
Yet there are also strong connections to what's come before; this parable isn't just about avoiding the idolatry of money. It is about that, but it's also clearly about the kingdom of God (verse 9). So once again, this isn't a moral lesson but more of a teaching on who God is and what He's like. In other words, the "first/main character" isn't the dishonest manager. (Here again, we get our clue from the first character mentioned: not the manager, but the rich man/lord/master!)
The manager "gets away" with his dishonesty only because he staked everything on the mercy of the master. The master by rights should have immediately imprisoned the manager when he discovered the wasting of the rich man's possessions (that wasting connects us to the younger son of Luke 15's main parable). But he gives the manager time to settle things. And when the manager hatches and executes his plan to save himself (another connection back to Luke 15's younger son), the master actually commends his shrewdness! The manager has put the master into the position where he essentially must honour the "debt write-downs" (which are huge amounts of value) in order to still be the merciful one in the eyes of the other debtors.
Again commentator Arthur Just puts it well:
If one considers the parable from the lord’s perspective, then the focus of the parable is not on the dishonesty of the steward, but on the mercy of the lord. This assumes that the lord is an honorable man, which seems to be the pattern of the households in Jesus’ parables. The rich lord’s mercy to the steward who squandered the lord’s estate (16:1)…is parallel to the father’s mercy to the prodigal who squandered the father’s inheritance (15:13…[same Greek word as 16:1]). The purpose of the parable, then, is to reveal the lord’s mercy.Arthur A. Just Jr., Luke 9:51–24:53, Concordia Commentary (St. Louis: Concordia Publishing House, 1997), 614. [Emphases original]
The Pharisees continue to fall into the pattern of Luke 15's older brother: they scoff at the mercy of the lord towards the one who squanders the wealth, and that sqaunderer too! But Jesus knows their hearts and calls them out.
And then He draws them into the larger story of salvation. Remember, they had rejected John and his baptism (7:29), and were focusing on making themselves righteous before people, rather than actually believing and teaching Torah which was God's own Word to them and to the people they were supposed to lead. And so another sense of the parable is the Pharisees themselves were not only seeing money and earthly wealth wrongly, and therefore squandering it, but they were also squandering their spiritual leadership of the people of Israel by focusing on themselves rather than on the Word of God.
This also helps us connect the statement about marriage; especially in the way that many Bible editions format this verse 18, it seems disconnected and out of context. But it flows from what comes before and into what comes next. Yes, it is a statement about earthly marriage, and seems far more severe of an interpretation of Torah certainly than Moses, and even of Jesus' own other statements which allowed exceptions. But in context it is also (and maybe even more importantly here) a reminder that earthly marriage is a picture of the relationship between God and His people (e.g. the book of Hosea, Ephesians 5:22-32). So this verse is also (primarily?) about spiritual idolatry; those who act towards God the way that a man acts towards a woman in wrongly divorcing her and finding someone new are in fact not only adulterers, but idolaters.
The parable of the rich man and Lazarus is another connection to what's come before. Yet there is a stark difference. The first/main character mentioned is a rich man, yes, just like before, but he doesn't represent God in this case! Luke has just reminded us that the Pharisees were "lovers of money" (16:14) and so Jesus, in response to their scoffing, now targets them even more strongly in this parable.
The self-righteous rich man has his earthly rewards and comes to find that what he had in the earthly life was the only reward he would have (think back to the blessings/beatitudes and woes in 6:20-26). But the poor man Lazarus, who had no earthly wealth, received in eternity all the good things he lacked on earth. This is another application and illustration of verse 15: what people value on earth is not what God values.
And then, we see that the rich man still clings to his self-righteousness, even in the midst of torment. He doesn't address Lazarus but Abraham, since he sees himself as a favoured child of Abraham (recall John 8:31-59). He doesn't truly repent but just wants physical relief (back to Luke 15's sons). And he continues to stand not on Jesus as the One who is ushering in the new kingdom (back to verse 16-17) but on Torah, or more properly, the misuse of it in terms of clinging to a self-righteous understanding of it instead of letting it point them to the One who is the fulfillment of it (e.g. Romans 10:4 - Jesus is the end/fulfillment/completion/goal of Torah.
And then Jesus once again masterfully connects Old and New: both Law and Gospel is God's Word, and if someone rejects God's Word under the Old covenant, why would they treat the New any differently? Here again we are led to the idea of "hearers of the word" in Luke's Gospel account; Jesus' words find their mark, "if they do not hear [that is, hear, understand, and believe] Moses and the Prophets [that is, Torah] neither will they be convinced if someone should rise from the dead" (16:31). Of course, this points to Jesus' own death and resurrection; how many of the Pharisees who had rejected Jesus prior to His death and resurrection came to receive the truth after it? A few perhaps. But we know, even from Luke's second volume (Acts) that many didn't.
An Excursus (Side-Note) on Torah
We're indebted to Dr. Just once more as he points us to H. Hummel's excellent comments about how we should understand Torah. Spoiler alert: it's not just law, as in commands.
The true meaning of “Torah” is most succinctly defined by H. Hummel:
The conventional translation of “Torah” with “Law” is most lamentable.… If it were possible to turn back the clock and expunge fateful and misleading renditions from our Bibles, this would surely be the place to start. It indisputably is one of the major culprits in reenforcing the stubborn prejudice that somehow the Old Testament is more “legalistic” than the New, or at least contains proportionately far more “Law” than “Gospel.”
If it were possible, it might be better not to translate, but simply to transliterate “Torah,” as is the common Jewish practice. Short of that, it must be shouted from the housetops that, to the extent that we must settle for a single-word translation, “Gospel” would be far more accurate than “Law.” But that must be immediately qualified: Torah means “Gospel,” not in its narrow sense of the obverse of “Law,” but in its broad sense of both Law and Gospel.…
Alternatively, “Word of God” would often be a superb “dynamic equivalent” of Torah, because God’s Word always confronts us in both Law and Gospel.Arthur A. Just Jr., Luke 9:51–24:53, Concordia Commentary (St. Louis: Concordia Publishing House, 1997), 627.
With this understanding of “Law,” then, Jesus’ words about not “one little hook of a letter of the Law” falling away are directly linked to his announcement that the kingdom is now being preached in the ministries of John and Jesus. The content of the kingdom, that is “Gospel,” certainly was testified to beforehand also in the Law and the Prophets (cf. Rom 1:2; 3:21). But now the Gospel is enfleshed in Jesus and everything in the OT is established—interpreted through him!