Why are logos, pathos, and ethos used in an argument?

Logos: Since this is for logic it can show the audience that they know what they are talking about (using facts to persuade their given audience).Pathos: This is based on emotion, they can persuade an audience to help and abused animals or give to the homeless.Ethos: This is credibility, if someone uses this they'll have the audience make sure they know what they're talking about (a doctor talking about a disease).