John 2:7

Jesus saith, &c. S. Chrysostom asks, "But why did He not Himself fill the waterpots with water, and then turn it into wine?" He gives the right answer, saying, in order that He might have them as witnesses to the miracle who had drawn the water, lest any fraud or trickery should be supposed.

To the brim : lest, if any vacant space were left, Christ might have been supposed to have poured wine on the top of the water, which might have communicated the flavour of wine to the water underneath.