We know that the ideas of kol ram and peh malei have very effective results in tefilla and in learning.

Rav Yisroel Salanter used to emphasize numerous times that the only way to truly acquire yiras Shamayim, to truly inculcate it into our very beings is to learn mussar out loud, with a niggun.

In terms of realities, the fact that our bodies are completely physical and our souls are naturally spiritual, the marriage of the two is not really a natural relationship. Any additional work requires vast amounts of effort and continuous input just to keep the two realities from rejecting each other.

Music is one of the only things that can bridge that gap; on the one hand, it is physical, made from physical motions or actions, and yet it is so powerful it has the ability to penetrate to a person's very core (Rebbe Nachman has many Torahs dedicated to this concept, and warns about the spiritual ills that accompany music that wasn't created with pure intentions).

In order for mussar to really make an impact, we must learn it with a tune, a melody, more so than the singsong chant we have when we learn gemara.