Drastically.

You could wake up in the morning not knowing if you're still alive in the evening. Now, one could say that this was a normal part of life back in the 14th century. But not this. Because the plague killed everyone. Not only the poor, the working class. Even Kings and Queens and also the clerics.

Let's start with the obvious factor: The illness itself.

People didn't understand the plaque. They didn't have our scientific knowledge and had no idea what germs, bacteria, viruses are. So when they saw people, their loved ones spit out blood, having highest fevers, they didn't know what to make of it (except for the obvious "well, you're about to die"). If you catched the bubonic plague, the black knobs add to the list and the sight. Since people didn't understand it, they thought of many different things as a source for this. Staying within the very basic scientific reasoning, one of the reasons people could think of were invisible worms.

Now, when you imagine how people must have looked, you've got a basic idea how hard it must have been to nurse them. Especially when you saw that even the professionals were disgusted and didn't do a good job: Most people died anyway, no matter the care taken of and to them. So the master of a farm could die and the next in line could lie besides him, experiencing the same fate. Who cared for the women, the children, the animals? That uncertainty was highly immoralizing.

And don't forget that it was consens that if you're hit by such an illness, such a condition it was God's will.

This is where we're coming to the next part, the religious component:

As mentioned, people thought of illness and famine as a punishment by God. Be it for crimes in thought or in deed, be it for bad behavior, for not respecting the Lord. Heresy, simony come to mind. And that was a crucial turning point for society back then: the plague hit everyone. The devotional priest as much as the cardinal who was known to be... Let's say not as much on God's good side. It hit the workers as well as the Kings.

Now, with God punishing everyone, what does that mean? People didn't know, they were insecure about it. Praying together so things might get better would get you killed. Not doing so, too. Nobody knew what their deity wanted to tell them, so they came up with their own solutions and ideas.

One was to find someone they thought responsible. That led to pogroms on the European Jews, to murder. Some hunted and killed priests they thought guilty of crimes against the church. It also led to people become agonistic. Depressed. Cathartic. Their God had let them down and their whole world didn't make any sense anymore. So why bother at all?

Which leads to the biggest change: The breakdown of the economic system

To understand european medieval society of the 14th century, you need to know how it worked. First, there were the workers (peasantry). They farmed, bred animals, built and so on. They were the workforce and those who fed the country, so to speak.

Then there were those who prayed, the Clergy. They were the link to God, those who secured God's will to be followed. They also supported the peasantry with doctors and nurses (they weren't known by that term back in the day, yet.). Abbeys were where the ill and injured found remedy. Most physicians were or came from clergy.

And then there was the Nobility, the fighting class. Those who defended from harm, who were sent to fight against the enemies of the king. But also, in times of peace, they were responsible to keep the peace of the land.

Suddenly all that broke away.

The clergy didn't preach anymore. They weren't able to comfort people. They weren't able to heal, to be a link to God. Because they either died themselves or secluded from society. Churches closed or burnt down.

Then, the fighters died or ran away. Remember, everyone could die because of the plague. So those with a better education had a better idea of how to (re)act to it. So they took they stuff and went to a journey like a pilgrimage. Or just away from others.

Now, think like a worker: When the Clergy doesn't pray anymore and the fighters don't fight, why the fuck should I work? Or to be more precise: Why should I work for the lord I used to?

Within the 14th century approx. 70% of the European population died. That left gaps in every profession, in every of the three estates. The peasantry now had a certain range of choice. They were more free, and what's more important: They were less to be followed, catched and forced back to their old master. Not only did their whole idea of how things should be arranged change, their day to day life now brought them more danger but more possibilities, as well than ever before.