Our Gemara used a word “Tefufos” to refer to the manner in which the ketores was gathered in the Cohen’s fist. Tefufos means full to the point of penetration between his fingers but not bursting out. Rashi provides the etymology for this word from a Mishna in Avos 2:6

אַף הוּא רָאָה גֻלְגֹּלֶת אַחַת שֶׁצָּפָה עַל פְּנֵי הַמַּיִם. אָמַר לָהּ, עַל דַּאֲטֵפְתְּ, אַטְפוּךְ. וְסוֹף מְטִיפַיִךְ יְטוּפוּן:

Moreover he (Rabban Gamliel) saw a skull floating on the face of the water. He said to it: because you drowned others, they drowned you. And in the end, they that drowned you will be drowned.

The translation drowning is really not a perfect translation because why would Rashi use it as an etymological proof for Tefufos?  Remember, drowning implies total immersion and Tefufos was supposed to be an expression of the fist holding an amount that is full but not overflowing. Thus, the phrase used for drowning really had a different implication, such as floating just beneath the surface.  

The Lechem Shamayim (Avos 2:6) notes this textual problem, as well as some others, such as why discuss a case of drowning altogether?  Are there not many other ways for bandits to murder?  The answer is Rabban Gamliel was hinting at the concept of Gilgulim, reincarnation or the more scholarly word, Metempsychosis.  The person who committed murder would end up floating just beneath the surface, meaning that his or her soul would not achieve peace and would still end up searching for its repair and correction.

The idea of Gilgulim is appealing psychologically because punishment becomes less about punishment and more about finding a way to correct what has been wronged.  Furthermore, psychologically, we can understand that every sin is a small death, a small exile, and our souls begin to wander at that very moment.  Whenever we are unhealthy and commit falsehoods our souls know it, and the process of alienation and wandering begins.  Our only way forward is to find our way back.