Really need help describe the radical design of john steuart curry painting baptism in kansas

They are shown in art because art is made to express absolutely everything you want. For example in art everything you use is important because if you are mad you could probably use red or black in your art. Or another is that facial expression and body language can tell/ show others how  you are feeling and art is exactly like that. That's why celebrations and rituals are shown in art.

Hope this helps and that it's right <3 :))