Later, metta just becomes a part of your life. All the time you will remain suffused with love, compassion and good will. This is the aim, the goal. The path of liberation is the path of working at the deepest level of the mind. There is nothing wrong with giving good mental suggestions, but unless you change the blind habit of reacting at the deepest level, you are not liberated.
Nobody is liberated unless the deepest level of the mind is changed.
And the deepest level of the mind is constantly in contact with bodily sensations. We have to divide, dissect and disintegrate the entire structure to understand how mind and matter are interrelated. If you work only with the mind and forget the body, you are not practising the Buddha s teaching. If you work only with the body and forget the mind, again you are not understanding the Buddha properly. Anything that arises in the mind turns into matter, into a sensation in the material field.