If you want to overcome your karma, change your vibrations.
Chanting a mantra tunes you into the experience of the particular mantra. This alignment allows you to experience this vibration by becoming the vibration. The more sensitive you are, the deeper you will experience the effects. Also, the longer and more focused you chant the mantra, the more impact it will have on your consciousness.
It is not only mantras that have a strong impact on your being, but every vibration is crucial. When you think negatively, you create a subtle vibration. The longer this vibration persists, the more it affects your being; the vibration of the thought then creates an emotional vibration, which generates a vibration in the physical body. This is where all the sensations come from in the body.
When we talk about blocks in the physical or subtle body, such as in the chakras or the nadis where the prana flows, we are referring to areas where the vibration is out of alignment; areas that are vibrating slower than they should, and where the flow of vital energy is impeded.
In the same way that chanting mantras impact your being, so do your thoughts, words, and actions. This is how habits in your life become patterns. You create vibrations and then, consciously and unconsciously, you react to them. Repeating mantras can help liberate you from these ingrained patterns.