Mar 2:21 No man also sews a piece of new cloth on an old garment: else the new piece that filled it up takes away from the old, and the rent is made worse.
Alterantive: Also, noone sews a piece of unprepared wool onto an old garment: else the new piece, as it become fuller, pulls away from the old and the tear is made worse.

The exact same language is used in Mat 9:16. As then, the context is the difference between Christ and John the Baptist. The analysis of that verse is here and the vocabulary and concepts discussed apply here as well.

"New" is from agnaphos (agnaphos), which means literally "not fulled" referring to the process of abrading cloth so that it becomes fuller, softer, and warmer,. This process is used specifically for wool. Abrasion pulls the hairs in the woven cloth ("felting" is a similar process for unwoven wool) and tangles them. As the fibers are pulled together, the cloth gets smaller. When you wear, use, and wash a wool garment, it is naturally "fulled," which also make is shrink. Fulling is usually part of preparing the wool before it is sewn into garments because wear alone will full the wool, shinking it. However, in the simpler clothing of Christ's era, which required much less cutting, sewing, and fitting, clothes could be made with raw cloth and fulled by wear.

Christ used clothing as a complex symbol. It represents both wealth, which makes it a part of the mental realm, but it also represents a person's place on society, which is part of the emotional realm. However, wine, the symbol in the next verse, is also symbolic of the mental realm but is also has an emotional component.

The contrast of ideas from the mental realm are also here: the old Jewish tradition of holy men fasting and the new Christian tradition of eating and drinking, satisfying the body and the mind. There is also a contrast of emotions here: the sadness of the old traditional mourning of atonement and the new joy of the celebration of a bridal ceremony. The taking of Christ from his followers is a return to mourning, but it is only temporary because Christ rises again.

There is a strong sense here that things, in this case, wool cloth, get better with age, in this case, because it is made fuller. However, there is also a sense that things wear out over time, as in a piece of clothing that gets a tear in it.

Christ is saying that his message is new and his mission not complete. Fasting, suffering, and mourning is part of the process that will finish his mission, but that process will take time. He is also suggesting that the Jewish tradition had served its usefulness but that its time was at an end. It could be patched, but not with Christ's new ideas, which had yet to be completed.

Interestingly enough, the word translated here as "takes away," referring to the patch being torn away from the cloth, is the same word Christ used describing the bridegroom being taken away in the previous verse.

So Christ is saying that he is not a patch on the old garment of traditional Judaism. Because when the patch is taken away, it would rip the cloth. He is saying that he is something new entirely, new ideas and new emotions, which means new relationships. When he is taken away, his followers will mourn, but only for awhile, because his resurrection will complete something entirely new.

"Garment" is from himation (himation), which was an oblong piece of cloth worn as an outer garment. The term generally means "clothes" and "cloth."

"Take away" is from airo, which primarily means "to lift," and also means "to raise up," "to take up," "to raise a child," "to exalt," "to lift and take away," and "to remove."