Here's an introduction to the sefer copied from Wikipedia.

I did my own synopsis/quoting of the first perek. I am not going to say I will do this for the whole sefer because its very long and would take a long time, but this was very usefull for and I hope it can help some of you get a greater understanding of how important this sefer is.

The Mesillat Yesharim (Hebrew: מסילת ישרים English: "Path of the Just") is an ethical text composed by the influential Rabbi Moshe Chaim Luzzatto (1707-1746). It is quite different from Luzzato's other writings, which are more philosophical.

Mesillat Yesharim was written and published in Amsterdam. The earliest known manuscript of Mesillat Yesharim, written in 1738, was arranged as a dialogue between a hakham (wise man) and a hasid (pious person). Before publication, it was rearranged to have only one speaker.

Mesillat Yesharim is probably Luzzato's most influential work, forming part of the curriculum of virtually every yeshiva since being introduced by the Mussar Movement of Rabbi Yisrael Salanter.

The aim is the perfection of character. Unlike most mussar seforim, which are ordered by character trait, Luzzato builds his work on a Beraita (quoted in many places, including (Bablylonian Talmud, Avodah Zarah 20b)) in the name of the sage Pinchas ben-Yair, whose list goes in order of accomplishment.

Within each step, Luzzatto explains the step itself, its elements, how it can be acquired, and what might distract from its acquisition. For example: Watchfulness can be acquired by setting aside time for introspection, and acquiring watchfulness can be impaired by excessive mundane responsibilities, wrong company or a cynical stance in life. The same pattern is used for every single one of the traits mentioned.

First Perek of Mesillas Yesharim:

What is Man’s purpose and obligation in this world?

I think It is of importance to look at the title of the Perek. The Mechaber uses the word “Be’Olamo”, HIS world, not THE world. We each have our own world in our own eyes. We each have a special connection with Hashem that nobody can replicate. This is my world. Hashem loves ME.

The first line of the sefer gets right to the point. It is out job here to figure out what our purpose is in this world. What are YOU doing here? Hashem didn’t just create you to fill the world with humans. YOU have a purpose. YOU were created for a purpose. This can often be a lifetime mission, but it Is essential to your Avodas Hashem. I always kind of overlooked this and took it literally. I think that Ramchal is telling us more in this line than just a fact. Its not only that we need to figure out our purpose here in this world, we should all realize there IS a purpose for all of in this world as long as we are here. This is important for our self esteem when it comes to improving ourselves. We cannot get down on ourselves and think we are worthless people because we sin. Hashem knows we sin and does not expect us to be perfect. Perfection is only attained by Hashem Himself. Achieving goals can be attained by us mortals. Perfection cannot.

True Hana’ah in this world does not come from physicality. It doesn’t come from anything other than the Ziv of the Shechinah. There is no greater joy. What is ‘Ziv Hashechinah’? It is recognizing the beauty of Hashem through everything. Not just the good, but the (seemingly) bad as well. What is else is ‘Ziv Hashechinah”? Its being Besimcha. Being Besimcha Tamid because of a Mitzvah. “Mitzvah Gedola Lihyos Besimcha.” I hear from a friend that the opposite is true as well. “Simcha Gedola Lihyos Bemitzvah.” Its appreciating the opportunity to do a Mitzvah given to you by Hashem. The ‘Ziv Hashechinah’ is always there, we just need to recognize it and benefit from it. However, the true source of the Shechinah is not this world. Its Olam Habah.

There is but one way to get to Olam Habah. That is going through this world and doing the Mitzvos that were placed here by Hashem. The ONLY place to get the opportunity to do these Mitzvos is this world.  Ramchal says if you look further into the matter, cleaving to Hashem is absolute perfection. Anything else that we PERCEIVE as good is none other than nothingness. Being close to Hashem is the only REAL and TRUE good in this world. It is attainable through Miztvos. Don’t think that because we aren’t the Gedolei Hador (yet) that we cannot attain closeness to Hashem in our ways. It is non-Jewish to believe this. For a person to be Zocheh to this closeness to Hashem he must work at it. Nothing is given for free here. Ramchal uses the words ‘Ameilus’ and ‘Hishtadlus’. Those are two very strong words for this. Ameilus is really getting into it. Its rolling up your sleeves and being willing to get dirty. Hishtadlus is truly believing that you have done all you can and the rest is up to Hashem. That means not being lazy. Be Ameil and Mishtadel in your Mitzvos and you WILL get the Shleimus Ha’amiti of being Dovek to Hashem.

Opposite all of these Mitzvos and opportunities to grow towards Hashem, were placed Taivos and physical desires. These are the things that distance oneself from Deveikus Hashem. Every situation in life is a Nisayon. We have the option to choose one way or another. Every time we pick the Mitzvos and Avodas Hashem, we bring ourselves that much closer to Hashem. Every time we choose the Taivos and physical desires, we distance ourselves from Hashem. 

Here is the underlying idea here. Man was creating for Olam Habah. Not Olam Hazeh. However, in order to get to what we were created for, we must first spend a lifetime in this world in order to get to the next world. It is impossible for an intellegent person to think that our purpose is for this world. People never attain TRUE happiness here. We have so many Tzaros and sicknesses in this world and after all that is death! No, this world is just my waiting room. I am here to prepare for the next world. Maybe someone will live 100 years here! That's considered a long time. But in the next world everyone is eternal.

Another reason why this world is nothing compared to the next world is the fact that we have such precious Neshamas. Our Neshamas get no Hana’ah from this world so why would they be created if the next world wouldn’t matter?

After knowing now all of this, it is quite easy to understand why the Mitzvos are so important to us. They are individual pearls that are so precious; there literally is no price on them. Even a minor change in the outlook or the kavanah of the Mitzvah, can have a huge impact on our real purpose, Olam Habah. Therefore, we need to learn the Halachos of each individual Mitzvah. As Ramchal says, a gold salesman is so precise when he weighs his gold, so why shouldn’t we be?

We can now see that the main reason for a person to be alive and well in this world is only to fulfill the Mitzvos  and stand up to the test when there is a Nosayon. The worldy pleasures, and I mean the Mutar ones, are only here to aid is in our mission of Deveikus Ba’Hashem. We eat to live. Sleep to serve Hashem better. Make Parnassah to build a family and support our Torah. But every action should be directed towards Hashem. Big or small. Anything that will distance us from getting closer to Hashem should be shoved away and avoided.