Citta is a Pali and Sanskrit word which is most usefully understood as the English word heart, or heart-mind. Unlike Manas, another Pali word that refers to the intellectual processes of mind, Citta is more of the emotive, felt sense of the mind. For this reason, heart is the most useful English word for Citta to be translated to as everyone can relate to the emotive, felt sense of the heart.
The Citta is very open and receptive to what it comes into contact with. It takes on the characteristics of what it is being touched by--like water taking on a color when dye is put into it. It also begins to take on more lasting (as opposed to momentary) characteristics when it repeatedly comes into contact with something. For instance, if anger frequently touches the Citta, the Citta will begin to be shaped by anger and begin to flare up in an angry response to whatever or whomever it may be coming into contact with. We all know someone who is an “angry person” or someone who is a “kind person.” These people’s Cittas have been very much shaped and conditioned by anger and kindness. Our understanding of this paves the way for cultivating the tone of our own heart-mind and reconditioning from reaction to response. In a word : freedom.
Citta and the body have a very close and sympathetic relationship. The state of one almost directly affecting the state of the other. So, from the above example, when the Citta is effected by anger, the body responds by, say, having a tight stomach. When the body is relaxed and at ease, the Citta is much more likely to have those same characteristics. Due to this very close relationship, we can form the Citta in skillful quantities by cultivating those same skillful qualities in the body.
If we wish to train the Citta to not rush out into the world of sense contact (including mental sense contact of thoughts and images) and abide in a restful ease within the present moment, we start with the body. This is one reason why an important aspect of the Buddha’s path to awakening is cultivating mindfulness centered in the body. We create a body that is calm and at ease, resting at home on the earth. This creates a home, you might say, where the Citta can rest in the present moment and be nourished by those same qualities of body, taking on and being shaped over time by those qualities.