When I first read this story I thought it is some zen philosophy which is complex to understand. After some time, I again came across same story and with a deep thought, realized what it means.

It means earlier zen master was doing it unconsciously, now he is doing it consciously.

Before enlightenment it was a burden for him. After enlightenment, he still had to chop wood and carry water and while he was doing the exact same thing, his perspective was totally different, it wasn’t a burden at all, it was a beautiful part of life.

Moral of the story:

Whatever we do in life, it doesn’t much matter, it is the state of mind that we do it in, that matters.
The story tells us that our day to day life, physical circumstances may not change much for us, on the pathway to spiritual journey, but our perspective may change immeasurably.
We should not expect a big difference in what we do prior and after during our spiritual endeavor.

The activities that we do in daily life, we have to continue doing them as it is.

We might be working at the same job and living in the same house, traveling same way, eating same food, working with same people, doing same work and still be a new person. The change is internal first, and external second.

The purpose of existence for the follower of spiritual endeavor is simply to live an ordinary life, but with mindfulness.

For most of us, everyday actions are done habitually, without thinking. According to Zen, this lack of attention is evidence of a separation between the individual and the world around him or her. We are always looking ahead to what will happen in future or looking what happened in the past, instead of experiencing the present moment.
Mindful attention to everyday activities provides an awareness of the present moment, and the opportunity to recognize the peace within both in self and other.

"Before Enlightenment - chop wood, carry water;
After Enlightenment - chop wood, carry water."

Old Zen saying