Lines 4 to 7 deals with his concept and outlook about life. He says he does not know Brutus's or others' point of view about it but for him, life is not to be lived only for his own personal honor or gain.
In lines 8 to 10, he begins to compare himself and Brutus to that of Caesar's status in life, showing their similar conditions as free men and that they are fed well and they endure the same cold winter.
Then he narrates his past experience with Caesar when they both swam the "angry flood" of Tiber. He proves that Caesar is physically weak because he almost drown had it not for Cassius' help. He magnifies his own capabilities by mentioning his glorious ancestors: "I, as Aeneas, our great ancestor, /Did from the flames of Troy upon his shoulder/The old Anchises bear, so from the waves of Tiber/Did I the tired Caesar."
After which he contrasts their present political positions: that of Caesar being exalted while he, Cassius, is to bow down before the "god" Caesar like a "wretched creature" of lowly position. He is like to one who is so low, begging for Caesar's recognition even just a nod from him.
Then again he cites another proof of Caesar's helplessness in the past and Cassius' second attempt at saving him. ...