The themes of the preceding chapters continue (as we continue to remember that the chapters and verses are not part of the original text) as Jesus continues His journey towards Jerusalem and ultimately towards His suffering and death for the sins of the world. Most of this chapter is spent at a dinner party, where Jesus again is bringing a right understanding and application of Torah to the Pharisees who largely lacking those things.
The Pharisees are here "watching Him carefully" even while at the same time inviting Jesus to dine with them; their hypocrisy continues. And while there, Jesus heals, as He so often does. But this time, He issues a direct challenge to those who are opposing Him: before He heals the man, He asks them if it's "lawful". This doesn't mean "illegal" as we would understand it, but lawful according to Jewish law, according to Torah. To do work on the Sabbath was prohibited. But, the question then comes, what is "work"? Many took a legalistic approach, defining "work" according to things like how far a person could walk before it became "work" and therefore was not lawful.
One interesting thing is that healing was never prohibited on the Sabbath. Jesus and the Pharisees have already clashed over this very thing, and it's underscored once again by Jesus, even turning it back on them (14:5). And they simply couldn't refute Him because they would know that healing wasn't actually prohibited, but couldn't admit it because of their pride.
However, the true significance of healing on the Sabbath goes deeper than being correct about what is and isn't lawful. The purpose of the Sabbath day was never about a legalistic "you must not work". Rest, properly understood, is restorative. The point of stopping work is recreation: re-creation. In that way, healing on the Sabbath is not only not prohibited, but it's a fulfillment of Sabbath. This, of course, was precisely what Jesus came to do: it wasn't only about "getting it right" when it came to understanding and teaching Torah, it was about actually fulfilling it in its entirety.
Humility and servanthood are the way of Jesus. For His disciples, they are fruits of faith. For those who seek honour in earthly ways, they will have received their reward if they get it. And then what's left? (It's the same thing Jesus teaches in other places (e.g. Matthew 6:1-6).) For those who have faith in Christ, they know that they have honour and favour from God, and an eternal supply of it from Him Himself, and so they don't need to seek it on earth.
That same principle holds not only when attending a banquet, but also when giving it. Here it's important to also see the eschatalogical (the end-times/eternal) perspective of what Jesus is doing and saying, not just the earthly one. We'll come back to that in a minute, but let's consider this in an earthly applicaiton. We would be wrong to apply this to ourselves by thinking that Jesus prohibits any of His disciples from ever enjoying a meal with friends and/or family, because that could be somehow repaid later on! The context is important; if a person throws a dinner (for example) with the goal of being seen as important because important people are there, or with the goal of currying favour with the guests so as to be repaid in like manner, then the motivation is turned inward on oneself. It's the same kind of thing as earlier: seeking an earthly reward, and (perhaps) receiving it.
The disciples of Jesus can certainly take this command of Jesus literally and have dinners for those unable to repay. And that generosity can manifest itself in different ways too. But that's the point: generosity is just that—generosity—when it flows freely from what has been received with no expectation of repayment. To expect repayment is no generosity at all, and if the desire for repayment is secret, then not only is it not generous, but it's hypocritical too; a person wants to appear generous without actually being generous.
But more than a lesson in generosity, this teaching of Jesus is actually eschatalogical. That is, it's a statement on how God acts, and what the results of that are in eternity. Jesus gives us this "both/and" perspective by introducing the resurrection (14:14). And when someone grabs onto that to bless those who will have eternal table fellowship with God (14:15), Jesus extends His teaching into that eternal perspective.
In that sense, this section of 14:15-24 calls to mind the end of chapter 13, where those who were invited to see Jesus as Messiah rejected Him. Here this same invitation is being framed as table fellowship. Those who aren't at the banquet are those who were invited but who rejected it, putting other things before this amazing invitation to receive a feast at no cost to themselves.
It also continues the theme of the "great reversal" that we saw in 13:30 and in 14:11: those who see themselves as first, as greatest, will find that they aren't in fact that. Those who recognize that they are the last, the least, they are those who actually find themselves in a place of great honour.
A great temptation is to perceive the word "hate" here in a way that it's not intended. Arthur Just, in his commentary on Luke, puts it this way:
These words jar our modern ears, where the human kinship of the nuclear family has such a lofty place, even within the church (see also the Fourth Commandment; Eph 6:1–4). Does Jesus really mean that we are to hate our father and mother and wife and children and brothers and sisters, even our own soul? Matthew records the softer formulation that makes “hate” correspond to “not love more than” (Mt 10:37), i.e., we are not to love family “more than” Jesus and his kingdom. This is, in fact, the meaning of “hate” here, but Luke preserves the semitic [Jewish] expression in all its hardness.Arthur A. Just Jr., Luke 9:51–24:53, Concordia Commentary (St. Louis: Concordia Publishing House, 1997), 580–581.
The context is that of the cost of discipleship. To follow Jesus is to put everything else—including our closest earthly relationships—in a secondary place. Of course, many of these relationships are gifts of God Himself, but they dare not overtake Him in our lives and so become an idol and a barrier to entering the feast of the kingdom of God.
Keep in mind that these words are spoken to the "great crowds" (14:25) who were accompanying Jesus. When crowds arise, Jesus brings up the fact that following Him isn't an easy thing (another example is in John 6). The tendency is for people to have what we call a "theology of glory", thinking that life as Jesus' disciple is a way to have an easy earthly life. But nowhere does Jesus promise that; in fact He promises the opposite (see also John 16:33).
The last couple of verses sum all of this up. Our first thought as modern readers about salt is simply as a seasoning. But it was used also as a preservative in a world without electric refrigeration, and so there are both flavouring and preserving qualities when the Bible references salt. So one who has been the salt of the earth (see also Matthew 5:13) and who loses that in an ultimate way (in favour of other things such as riches, family, etc.) is one who loses even eternal salvation.
The final statement in this chapter returns us to the theme of being hearers of the Word. Those who have the spiritual ears—those who can hear this, believe it, take it to heart, and act upon it—let them do so.