This is a proverb to be understood from a Buddhist side (not to call to murder a prophet like some might understand it).

This simply means that Buddha carried a message to his followers. Once the followers (the Budhists) had well integrated the message into their own understanding and are able to come intuitively to their own conclusion for their own life, they had to go over the teacher and follow for themselves what they retained of the learning instead of asking Buddha what he would say of it.

When meditating, if they see Buddha coming forward, this means there is a problem in the way they are progressing and should get this image discarded.

In no case should they let it come into a worship of the person Buddha over what they were meant to understand out of it. If their inner voice said a thing and Buddha another, they should not keep so strictly on what Buddha had said as ultimate truth and put his words into a cult.

This is not only true now for the Buddha followers, but also more specifically to any Jesus or Nobody worshipper (or whatever ancient God) who put words that were not specifically meant for their understanding or altered by time into a worship.