In many passages of the scriptures, it's mentioned how the process of devotional service is easy. Krsna Himself mentions that it is su-sukham kartum avyayam: it is everlasting and joyfully performed.
If the process of devotional service is so easy, why are we not pure devotees yet? Why do we have so much difficulty in advancing on such an easy path?
The problem is that although the process of bhakti is really very easy (especially if compared to the processes of self-realization practiced in other eras), the era we live in is so difficult that any process of self-realization, even the pure and simple process of bhakti appears to be difficult.
In Raja-Vidya (chapter 3), Srila Prabhupada mentions that:
"Practically speaking, this process is not very easy in this Age of Kali. In Śrīmad-Bhāgavatam a description is given of the people of this age. Their duration of life is said to be very short, they tend to be phlegmatic and slow and to sleep a great deal, and when they’re not sleeping they are busy earning money. At most they only have two hours a day for spiritual activities, so what is the hope for spiritual understanding? It is also stated that even if they are anxious to make spiritual progress, there are many pseudospiritual societies to take advantage of them. People are also characterized in this age as being unfortunate. They have a great deal of difficulty meeting the primary demands of life – eating, defending, mating, and sleeping – necessities that are met even by the animals. Even if people are meeting these necessities in this age, they are always anxious about war, either defending themselves from aggressors or having to go to war themselves. In addition to this, there are always disturbing diseases and economic problems in Kali-yuga. Therefore Lord Śrī Kṛṣṇa considered that in this age it is impossible for people to come to the perfectional stage of liberation by following the prescribed rules and regulations."
As we can see, the problem with Kali-yuga is that it drastically limits our attention span and make us constantly struggle for survival, always facing so many difficulties that it's hard to find time and energy for practicing spiritual life. Such problems have been exacerbated in the modern age, but the truth is that there was not a time when people didn't have difficult lives in the last 5000 years.
However, we should understand that this is exactly the test. Sri Caitanya Mahaprabhu gave us a process that is adequate for the amount of difficulties we have in this era. The situation is now very difficult, and thus the process is very powerful. If one can surpass the pressure of immediate needs and practice devotional service in a mature and determined way, in association with other sincere devotees, it doesn't take much for one to go back to Godhead. Even for the ones who fail, there is the perspective of another birth in a rich or pious family, where one will have better opportunities to continue from where he stopped.
A rich family gives one the opportunity of receiving a good material education and living without the need for fighting for basic survival, while a birth in a pious family gives one good moral values that can serve as a foundation for a life of devotional service later on. Both situations have certain dangers, but they offer better opportunities than most of us had in this life.
This shows how the process of devotional service is indeed powerful and how we should make it a priority in our lives since even a relatively small advancement in the path can give us so much benefit.