Is "'cause" necessary in this sentence? Can I only use "if" in this sentence? How does the meaning get changed?

Rebecca

"Cause" here is a shortened version of "because", and it is not necessary in this sentence. Both "because" and "if" in this case are used to give explanations or reasons for something. Since "if" exists here, you do not need "cause" or "because". "Cause" just helps emphasize the fact that there is a reason for something.