“Have you never read what David and his followers did..." (Mark 2:25-28)

“Have you never read what David and his followers did when they were hungry? How he went into the Temple of God in the time of Abiathar the high priest and ate the offering bread – which was only permitted for the priests to eat – and also gave it to his followers? The Sabbath was made for man – not man for the Sabbath. Therefore the Servant of Humanity is also master of the Sabbath.” (Mark 2:25-28)
Here is the context and the question Jesus is responding to:
Then later he was traveling through corn fields on the Sabbath. As his disciples were walking, they plucked some ears of corn. Then the pharisees asked, “Look, why do they do what is not permitted on the Sabbath?” (Mark 2:23-24)
Jesus is comparing the fact that his disciples were eating grain on the Sabbath - which is normally forbidden by the Mosaic custom - as indicated by the Pharisees.

Were they followers or companions?

Note the word "followers" is often mistranslated to "companions" in some translations. The word comes from the Greek word μετά (meta) - which refers to someone who is coming after - or following. In other words, this word is best translated to "followers,"

So Jesus is making a direct comparison - between Jesus' followers and David's followers.

Jesus is also indicating that his disciples were hungry. It should be noted that Jesus and his disciples were traveling from town to town in order to spread the teachings of love for the Supreme Being. Jesus and his assisting students were traveling through harsh terrain and thus needed to eat in order to keep their strength - just as David's followers were "in need."

This statement indicates that David was outside of the mainstream institutional Mosaic priesthood just as Jesus was. While both David and Jesus certainly accepted offering food to the Supreme Being as stated by each in other verses, it is indicated here that neither accepted the official positions within the Mosaic institutions. This is because God's representative is chosen by the Supreme Being.

What is the purpose of the Sabbath?

Jesus is indicating that the purpose of the Sabbath was to assist a person in their devotional practices, not become a replacement for them. The purpose of the observance of the Sabbath or any holy day is to remember the Supreme Being - especially for those who spend much of their time focused on the mundane things of the physical world. As such, taking the Sabbath or a holy day off of work and spending some time worshiping God will help purify our life and consciousness.

Instead of seeing this, some will teach that the observance of these days is spiritual life in itself. This is basically saying that the goal is to become disciplined for the sake of being disciplined. This makes no sense. It is like saying that disciplined is an aim within itself.

There are others who become disciplined so they can impress others. They are seeking the approval of others by utilizing religious principles to pretend to be somehow honorable or worth our respect. This is the lowest form of religiosity - one that was condemned by Jesus directly as he discussed some of the institutional priests:
"But all their acts are done in order to be seen by others: They widen their phylacteries and lengthen the tassels on fringes of their robes. And they like the places of honor at the feasts; and the important seats in the synagogues. And in the markets they like being called ‘Teacher, teacher’ by others." (Matt. 23:5-7)
Either approach - observing holy days as the end in itself or seeing them as a means to impress others - are condemned here by Jesus.

Furthermore, someone who is utilizing their time and strength to serve the Supreme Being has already accomplished the goal of the observance of these holy days. They are already working to please the Supreme Being.

Is compassion the same as sacrifice?

The Supreme Being is more pleased by those who are spending their time trying to communicate His teachings to others. This is true compassion according to Jesus. This type of service - geared to helping the spiritual lives of others - exceeds the various ceremonies and rituals. It is the prime service the Supreme Being is pleased with because He wants each of us to come home to Him.

The Greek phrase, υἱὸς τοῦ ἀνθρώπου is being translated to "Servant of Humanity" here. This is often mistranslated to "Son of Man." What the is a "Son of Man"? Every male is a son of a man.

Notice that Jesus is using the third person here. He is not saying "I am the master of the Sabbath." Why not?

Because Jesus is speaking of a particular role, not a single person. Consider that the Supreme Being called Ezekiel the same thing - again mistranslated to "son of man" - over 60 times. And David also humbly referred to himself with the same phrase - again mistranslated to "son of man" (Psalm 144:3). Job also referred to himself in the same way (Job 25:6).

These references can only be confusing for those who have mistranslated the term - because they don't understand what is the term refers to.

The Greek word υἱός (huios) can only mean "son" according to the lexicon, "in a restricted sense." Outside of this, it can also refer to "one who depends on another or is his follower." In fact, as indicated by the word υἱός used elsewhere to indicate servitude, for example:
“Can the servants of the bridechamber fast while the bridegroom is with them? They can’t fast." (Mark 2:19)
The word "servants" is translated from υἱός.
"But the servants of the material world will be cast out into the darkness – and there will be weeping and suffering.” (Matt. 8:12)
Here again the word "servants" is translated from the Greek word υἱός. These two verses and many others indicate that the word υἱός in this context doesn't always mean "son."

Rather, in these contexts, it means "attendant," "servant" or "follower."

In the phrase, υἱὸς τοῦ ἀνθρώπου we also have the word τοῦ meaning "of" and the word ἀνθρώπου which can mean "man" or "mankind" or better, "humanity."

Thus we arrive at the more appropriate translation of υἱὸς τοῦ ἀνθρώπου:

What does 'Servant of Humanity' mean?

This is the role Jesus is referring to: Someone who is serving humanity because he is teaching others about the Supreme Being and how someone can come to know, love, and serve the Supreme Being. This is the ultimate service to all of humanity.

This is also consistent with Jesus' statement:
"The greatest among you will be your servant." (Matt. 23:11)
This underscores the reason Jesus is referring to "servant of humanity" in the third person. He is not only referring to himself but also Job, David, Ezekiel, and other representatives of God - because they are serving humanity by giving people the teachings that help us come to know, love, and serve the Supreme Being.

In modern English, we have an expression, "master of ceremonies." What is a "master of ceremonies?" Is it someone who is in charge of the ceremony? No, it is the host or announcer at the event. The person who is leading the event, and setting the example for the event. Guiding those who are involved in the event.

This is the concept that Jesus is discussing. The master of the Sabbath is one who is empowered to serve the Supreme Being. Because serving the Supreme Being is serving all of humanity, such a person is exceeding the purpose of the Sabbath, and providing guidance for others.