Sree Sree Guru Gaurangau Jayatah!
Without firm belief, bhajan cannot be started. By serving Supreme Lord, Who is One, all are served. Sri Krishna Dvaipayan Vedavyasa Muni has given two analogies for this in Srimad Bhagavatam: (1) by pouring water at the root of the tree all parts of the tree are nourished and (2) by giving food to the stomach all the limbs of the body are nourished. The Supreme Lord is residing in the heart of every living being. So He understands whether a votary has got actual faith in Him or not. When there will be sincerity of belief, you will get the fruit.
In worshipping the Supreme Lord, it is essential to know that nobody on earth is to be blamed for our own difficulties. We reap the fruits of our own actions. Others are not the cause, although they may be instrumental. Dhruva, son of Uttanapad Maharaj, believed in the instruction of his mother Suniti Devi and after that the instruction of his guru Narada Goswami and effaced from his heart all hostile mentalities to anybody on earth and called God from the core of his heart. God was satisfied and as a result his father, his stepmother and all others, who were not congenial to him, started crying immensely in his separation. This is the difference between an ordinary aspirant for worship of God and a sincere devotee, who can immediately accept all the teachings of guruvarga and perform worship of God from the core of the heart. Ordinary aspirants hear many things but cannot accept those teachings from the heart. As God is Absolute Complete Reality, He is equal to all. He is naturally impartial. It is not the fact that He will grace to Dhruva, Prahlad, Ambarisha Maharaj and not others. Sun is giving light everywhere without discrimination of good or bad place. Some may accept the light for their benefit and some may not. What can the Sun do? Unconditional submission to the Lord is necessary to get His grace.
You will find in Prahlad's teaching that the nine forms of bhakti can be rightly practiced only with the fulfillment of the conditions (i) the worshipper should have the knowledge that he is of God or Supreme Lord i.e. with total submission to Him and (ii) it should be done only for His propitiation.
When we desire good behavior from somebody and do not get it, we become unbalanced. Desireless devotees are happy under all circumstances.
--- Jagad-guru His Divine Grace Srila Bhakti Ballabh Tirtha Goswami Maharaj