The context is important
This statement by Jesus in Luke appears to be out of context with the rest of his discussion, but the context of his statement is clarified in Mark 10:
Some Pharisees came and tested him by asking, "Is it lawful for a man to divorce his wife?""What did Moses command you?" he replied.They said, "Moses permitted a man to write a certificate of divorce and send her away.""It was because your hearts were hard that Moses wrote you this law," Jesus replied."But at the beginning of creation God 'made them male and female. For this reason a man will leave his father and mother and be united to his wife, and the two will become one flesh. So they are no longer two, but one flesh. Therefore what God has joined together, let no one separate."When they were in the house again, the disciples asked Jesus about this.He answered, "Anyone who divorces his wife and marries another woman commits adultery against her. (Mark 10:2-11)This gives us the context of Jesus' statement in Luke. Jesus is responding to challenges by pharisees - who were trying to test Jesus - or rather, trap him so they could find him guilty of blasphemy.
But within the exchange laid out in Mark we find an important point about Jesus' statement:
"It was because your hearts were hard that Moses wrote you this law."
The importance of time, circumstance and audience
Thus we find that Jesus taught the importance of time, circumstance and audience when it comes to the teachings of God's representatives. Moses, who was God's representative and teacher to those people, understood the condition of their hearts and this condition was assumed within his instruction.
So is Jesus taking a harder stance than Moses? No. It is understood by Jesus' statement in Mark that ultimately, God is pleased by honoring the marriage commitment.
After all, pleasing the Supreme Being is the ultimate goal of all the teachings of Moses, all the Prophets, and what Jesus really taught:
"For whoever does the will of my Father in heaven is my brother and sister and mother.” (Matt. 12:50)
“Not everyone who says to me, ‘Lord, Lord,’ will enter the kingdom of heaven, but only the one who does the will of my Father who is in heaven." (Matt. 7:21)
Therein we find the basis for any exception as well. Should the marriage be interfering with a person's service to God - pleasing God or worshiping God - therein would lie the exception for divorce.
This is because pleasing the Supreme Being is the sum and substance of all the instructions laid out in Scripture and by His representatives.
Many of us work hard to please those around us. We may want to please parents, kids, neighbors, bosses, work mates, fans, spouses and friends. Some of us work hard all our lives to please such people. Yet all of these efforts are in vain. Why?
Because others will never have the depth of understanding of what we went through to please them. And they will never be satisfied with what we do for them. Why? Because our pleasing them does not bring them fulfillment - and thus they are always seeking more from us no matter how hard we try to please them.
This is the nature of the material world.
No matter how hard we work and no matter what we accomplish, it is never enough. Everyone always wants more from us.
Why is this so? Because first of all, each of us is not the physical body we are temporarily residing in. Thus, no matter what these physical bodies receive in terms of attention, pleasure sensation or comfort - it will not satisfy us.
We might compare this to a person who feels sick one morning - and gets into his car and drives it to a auto care and detailing center. At the auto detailing center, workers may fix any problems with the engine and then clean the car, buff it, make it smell good, fill it up with gas and check the oil and fluids. But when the driver gets back into the car, he is still sick. The workers may have fixed the car, but they didn't do anything for the driver's sickness.
It is like this for the spirit-person who temporarily resides within a physical body. No matter how that physical body may be cared for or pleased by others, the spirit-person within is never satisfied.
Only love of God will make us happy
This is because the spirit-person within is only satisfied when we are tasting love for the Supreme Being. When we are involved in our original loving relationship with God we become fulfilled.
And what is the central component of any loving relationship? Pleasing the one we love. Love means wanting to please the one we love.
Jesus stated this clearly about his own relationship with God:
"By myself I can do nothing; I judge only as I hear, and my judgment is just, for I seek not to please myself but Him who sent me." (John 5:30)Jesus is most interested in pleasing the Supreme Being. Why? Because Jesus loves the Supreme Being. Jesus is involved in a loving relationship with God. So he wants to please the one he loves.
This also provides the understanding for another of Jesus' statements - one that has been grossly misinterpreted by those who have no entrance into the loving relationship between Jesus and God:
"I and the Father are one.” (John 10:30)When a person loves another person, there is a oneness between them. What is that oneness? It is a oneness of love. A oneness of will. Jesus is one with the Supreme Being because Jesus seeks to please the Supreme Being and thus they have the same wills. The same desires. What God desires, Jesus also desires. So there is a oneness between them.
This doesn't mean they become the same person - as many have incorrectly proposed. Just as two people who marry each other will have a oneness - they will still be two individuals. If Jesus is God, then who did Jesus pray to? And why would he also say as stated above, "for I seek not to please myself but Him who sent me." Simply to be sent by someone necessitates there being two individuals - the sender and the one who is sent.
But when one understands the loving relationship between Jesus and the Supreme Being, we can see the nature of their oneness. It is a oneness of love.
Jesus didn't just love God and keep it to himself either. He wanted others to also love the Supreme Being. He wanted others to become pleasing to the Supreme Being, because trying to please God never goes in vain. The Supreme Being sees everything we do to try to please Him and He is pleased with even the smallest effort to please Him.
It is not as if God always wants more and is never satisfied. The Supreme Being is self-satisfied. He is complete within Himself. Thus He truly appreciates any effort we make to please Him.
And such an effort to please God - when done with love and sincerity - fulfills us as well. This is what Jesus was sent to teach us - confirmed by his (and Moses') most important instruction:
“ ‘Love the Lord your God with all your heart and with all your soul and with all your strength and with all your mind’" (Luke 10:27 (and Deut. 6:5))