I will share with you the views of J.S.M. Ward on this subject
The inner meaning of the carpet is the chequered way of life-the alterations of joy and sorrow, of good and evil, of day & night, which we all experience in the course of our lives. Indeed, it may be said to stand for all opposites.
But what probably strikes the initiate more than anything else about this carpet are the four tassels which are woven into the pattern at the four corners. We are told that these represent the four cardinal virtues, but this is a late gloss (quite recent), probably invented towards the close of the eighteenth century, and there seems no particular reason why these should represent the four cardinal virtues more than the four elements, or any other particular four. We find the true origin of these tassels, as of many more obscure points in our ritual, if we study the mediaeval methods employed by the Operative masons when laying out the ground for a new building. The Master Mason, or Architect, as we would call him today, commenced his work by striking the center of the piece of ground on which the building was to be erected, and from it he plotted out the square or rectangle on which the containing walls were subsequently to rise. To do so, he extended ropes from the center pin to the four angles, and pegged these down at the corners of the building; by the simple use of square and triangle he was able to check the four corners and ascertain if they were true. As the walls rose, from time to time a piece of wood was extended from the corner inwards, and a plumb line dropped down to make sure that the walls were perpendicular and the angle as true on its upper tiers as it was at the base. A dim remembrance of those corner plumb lines lingered on well into the middle of the nineteenth century in Speculative Masonry, for I have met several old provincial Brethren who remember seeing, not merely woven tassels on the carpet, but actual tassels hanging in the four corners of the Lodge room; and in the ritual used in the old days it is these hanging tassels to which the four cardinal virtues were guides to enable a man to maintain an upright life. Like many other old and interesting customs, these tassels seem to have disappeared, and we are left with a symbolic representation of the four ends of the ropes which crossed the ground plan of the building.
Interestingly enough, I have seen these tassels both on the floor and in the corners of Lodge Rooms and simply thought that the Brethren had placed them on the floor for convenience. The paper presented above probably teaches us not to be so quick in finding solutions and digging a little deeper can be very beneficial.