The Article rejects the teaching that the Holy Communion is an offering again of the sacrifice of Christ. It also rejects the idea that such an offering is either needed or possible.
The background to this, at the time of the Reformation, was the practice of saying masses for the dead so that they could spend less time in purgatory. The idea that the Mass was a re-sacrifice of Christ was also linked to the doctrine of transubstantiation.
This is one reason the Book of Common Prayer did not use the term Altar for the Lord’s Table. The Holy Communion service also used the phrase “a sacrifice of praise and thanksgiving” to make clear that the Holy Communion is not a sacrifice in any other sense.
Dale