Why are the following lines central to the play?
all earthly things is but vanity. beauty, strength, and discretion do man forsake, foolish friends and kinsmen, that fair spake, all fleeth save good deeds . .

I think it's central to the play because All earthly things do not matter when it comes time to die, we leave behind our strength, beauty, etc. when we die.

It convey to the audience no to hold on into superficial such as strength and beauty and started to focus on keeping the core value that we held the most toward others.

The main man vs. man conflict in the outsiders is between the greasers and the socs, and specifically between ponyboy and bob in the fight in the park. in literature, conflict is a struggle between opposing forces.