http://www.ccel.org/ccel/mcgarvey/gospels.v.iii.html
Behold, the Lamb of God that taketh away the sin of the world!
Taketh = takes, is taking. Present tense.
Jesus is the Lamb of God who takes away the sin of the world. Not took away, in the past. Not will take, in the future. Takes away, right now. We sin. And our sins are taken away as they are committed, all the time.