There is a reason for abhyasa, practice. The intent of practice in yoga is to make the mind still, so that it is possible to go into the deepest meditative state, Samadhi. Without practice, the mind constantly jumps from thought to thought. But in samadhi, the mind stays perfectly still. When our mind is not still, its energy dissipates.
Here is a story by Swami Rama that explains further.
Long ago, when I was twenty-seven years of age, I opposed my master. After working hard I could not attain Samadhi. I told him, “Please give me samadhi.”
He said, “You are not yet prepared for Samadhi. If I pour a jug of water in a small bowl, it is of no use.” Then he said, “Okay; bring me a bowl.”
I brought a bowl. He said, “Give it to me and close your eyes.”
He made a hole in the bowl, gave it to me, and started pouring milk in it. Nothing would stay in the bowl.
I said, “Hey, what are you doing?”
He replied, “I am teaching you, but your head is like this bowl! If you have holes in your head, you cannot retain anything.”
(From Sadhana, The Path to Enlightenment, Pp. 201-202, by Swami Rama)
Practice is done to build the ability to keep the mind still, and to eliminate the tendency for the mind to move from thing to thing. Progress may be slow, but it is only by sincere, consistent practice, that progress is made.