All phrase which you're curious about is that meaning either "because" or "reason why". If I say "내가 아버지랑 닮아서 내 아들도 아버지랑 닮았다.". That means, "My son looks like my father because I look like my father". Additionally, if I say "내가 아버지랑 닮았으니까 내 아들도 아버지랑 닮았다.". That means, "The reason why my son looks like my father is that I look like my father." The front part of a sentence which is including "아서/어서/여서" or "니까" is the cause. I wouk like to help you this answer.

thanks~

참고: http://kr.hujiang.com/new/print/158350/