The word Hara is a form of addressing the energy of the Lord. Both Krsna and Rama are forms of addressing directly the Lord, and they mean “the highest pleasure, eternal.” Hara is the supreme pleasure potency of the Lord. This potency, when addressed as Hare, helps us in reaching the Supreme Lord.
The material energy, called as Maya, is also one of the multipotencies of the Lord, as much as we are also marginal potency of the Lord. The living entities are described as superior energy than matter. When the superior energy is in contact with inferior energy, it becomes an incompatible situation. But when the supreme marginal potency is in contact with the spiritual potency, Hara, it becomes the happy, normal condition of the living entity.
The three words, namely Hara, Krishna and Rama, are transcendental seeds of the maha-mantra, and the chanting is a spiritual call for the Lord and His internal energy, Hara, for giving protection to the conditioned soul. The chanting is exactly like a genuine cry by the child for the mother. Mother Hara helps in achieving the grace of the supreme father, Hari, or Krishna, and the Lord reveals Himself to such a sincere devotee.
No other means, therefore, of spiritual realization is as effective in this age, as chanting the maha-mantra:
Hare Krishna, Hare Krishna
Krishna Krishna, Hare Hare
Hare Rama, Hare Rama
Rama Rama, Hare Hare
Srila Prabhupada japa https://www.youtube.com/watch?v=dLD5CklJdPA