"Wash you, make you clean; put away the evil of your doings from before mine eyes; cease to do evil; learn to do well; seek judgment, relieve the oppressed, judge the fatherless, plead for the widow." (Isaiah 1:16-17)

God never intended the practice of religious ceremony to be the manner in which our sins are washed away. Christ accomplished that on the cross. It is finished!

Therefore, texts such as this one need to be considered in the context of the letter or book in which they are found. Isaiah is declaring that Judah needs to cease vain religious ceremony and practice true religion which is love and service to others.