He said that to Peter because 'fear' is from Satan. He is saying and showing that two wrongs will never make a right and to always make every choice in rightness. We are so imperfect so we carry with us not guilt or shame or feelings of inadequacies but of desiring to be accepted in the eyes of Jesus and God as he knows our heart of trying and never giving up to be better and strive to reach for his guidance to live more like he showed us to.