I have difficulties understanding Arnold's book of mathematical methods of classical mechanics.
Yet I should get some familiarity with the subjects found at chapters 3,4,7,8 before next semester to be able to participate in some courses. I will attach the relevant list of subjects found at the table of contents via a picture below.
The professor incharge claimed he studied the subjects from this book and does not know of a better reference (also claims he thinks chapter 3 and 4 are very clear, which wasn't the case to me)
As such I would be happy for literature references.
What can I do as an undergrad math student?
Are there any alternatives that are more comprehensive, and less difficult to read? Mathematically rigorous as well.

I'm a physics professor, and more mathematically inclined than your average physicist. Arnol'd is a beautiful textbook, but it is most emphatically not the one to learn Lagrangian mechanics from. (I used it as a student when I took a graduate-level class on the material.) Here are some texts that are often used for teaching Lagrangian & Hamiltonian dynamics in upper-division undergraduate physics classes:
To my recollection (though I haven't looked at Goldstein in years), none of these texts have the same level of mathematical rigor and rarefication as Arnold. If you pick one of the first two texts, there will probably be some material in Arnold that you will have not seen before.
There are multiple threads over at Physics StackExchange that might also be helpful, depending on whether you're learning the subject for the physics or for the mathematics: