Please explain the following quotation with reference to context "The old order gives way to the new lest one good custom should corrupt the world."

"And slowly answer’d Arthur from the barge: “The old order changeth, yielding place to new, And God fulfils himself in many ways, Lest one good custom should corrupt the world."

This quotation is from Tennyson's famous poem  "Idylls of the King" which deals with the life and adventures of King Arthur. These particular lines are from the section popularly known as 'The Passing of Arthur.'

"Bold Sir Bedivere," one of the most courageous 'Knights of the Round Table,' cries out in sorrow in the following words, just before the funeral barge in which the dying King Arthur has been placed  is about to sail away forever:

"Then loudly cried the bold Sir Bedivere: “Ah! my Lord Arthur, whither shall I go? Where shall I hide my forehead and my eyes?"

For now I see the true old times are dead,"

He laments that the institution of 'The Knights of the Round Table' has completely disintegrated:

"But now the whole Round Table is dissolv’d Which was an image of the mighty world."

It is then that the dying King Arthur feebly but stoically remarks:

"And slowly answer’d Arthur from the barge: “The old order changeth, yielding place to new, And God fulfils himself in many ways,

Lest one good custom should corrupt the world."

In history only one thing, namely, change is constant. King Arthur replies with calm fortitude to the inconsolable Sir Bedivere that however magnificent and worthy the institution of 'The Knights of the Round Table' might have been it is only appropriate in God's divine plan that it should pass away and give way to a newer institution because any institution which lives on and on will only become irrelevant and thus harmful to society.