It is very difficult to practice Dharma due to the habits of disturbing emotions that keep us attached to the worldly preoccupations of this life. It's as if you have to climb a mountain with a burden of heavy baggage on your back.
You have to undertake a very long and arduous journey in your Dharma practice, but it is very easy for you to lose your footing and fall down on the way. Furthermore, your fall back down again will be very swift, much swifter and further than for those who do not carry much of this kind of baggage.
When you climb up a steep mountain, it is very difficult and very tiring, similarly the practice of Dharma is also challenging. To achieve ultimate happiness you have to maintain Dharma practice diligently.
When you practice Dharma, you have to abandon any doubts and practice it with a single-pointed mind. There is no need to have doubts concerning Dharma, because since time without beginning, an ocean of practitioners have already attained enlightenment through this kind of practice.