Mark 1:4New International Version (NIV)

In Judaism “forgiveness” was achieved through the sacrifice of animals at the Temple in Jerusalem.  The Torah specifies this place alone can be used for sacrificial offerings, conversely no other place can be used.  The Temple was destroyed by the Romans in 70AD so the practice of sacrifice ended.  Today the Rock of the Dome sits over the spot where the Temple was so even today it is impossible to offer sacrifices.  This is the real cause of the tension over the presence of the Muslim mosque in Jerusalem.  In lieu of sacrificial offerings Jews can achieve forgiveness by prayer (this took the place of sacrifices I believe), good deeds and charity.

Note the obvious call to the latter by the Jesus of the Gospels and in particular the Epistle of James (highly controversial to Martin Luther, but little appreciated in today’s churches).

Regarding Mark 1:4 however, contrary to Steefen’s simplistic one-liner, the exact meaning of the latter half of that verse is not easily understood and is debated.  What brings the forgiveness of sins for John?  The baptism or the repentance?  How exactly dies it happen?  Is the ritual cleansing of the water the key?  There were many rituals involving water known from the ancient world and from Judaism in particular.  Temple priests ritually cleansed themselves.  The Essenes wrote about it in the Qumran scrolls.  Other cultures, such as the Egyptians, even went so far as to completely shave the hair from their bodies AND ritually cleanse themselves with water.  There’s far more to it than these few sentences, but this is the gist of the discussion of the matter.