Guidon is the first 'important' victim of the war, though the turning point will be another duel, much later, i.e. that in which the Muslim knight Solyman will kill the Christian Crusader Rupert - the man loved by Richard (yes, you read well) - mistaking him for Richard himself.
Guidon is, as well, the first enemy killed by Argantes after joining the Muslim army in Jerusalem. In Gerusalemme Liberata however the episode was much more powerful because the precious sword used by Argantes was the one Godfrey had given him to honor him as an ambassador; and the former, in addressing the Crusaders - and horrifying them - said that that very same weapon would soon kill the giver. In Gerusalemme Conquistata the beautiful scene of the presents for the ambassadors (Argantes and Aletes) has been deleted, but, on the other hand, this prevents Argantes from looking too ungodly. The Muslim knight here simply says that Godfrey has "despised" i.e. underestimated his sword, but it may prove dangerous to him too.
Argantes' quick "trascorrere," "passing by," possibly stresses his dangerousness by likening him to Dante's Cacus, a centaur+dragon creature (Inferno 25: 34).