I would like to know what "It was hard to move in." means in the following sentences:
Instead, the day of the Communion arrived. I could hardly sleep the night before, knowing that I would see him again. In the morning, I got up and washed my face with cold water. It was a sunny day in that one week of summer when fluffy white balls of seeds fly through the streets and cover the pavements, and the morning light is brilliant, almost blinding. I pulled on the white high-collared robe, which reached all the way to my ankles. It was hard to move in. I had to hold myself evenly and seriously like a monk. We got to the church early and I stood on the steps overlooking the street. Families hurried past me, girls in their white lace robes and with flower wreaths on their heads. Father Klaszewski was there, in a long robe with red sleeves and gold threads, talking to excited parents. Everyone was there, except for Beniek.
In this novel which is set in the 1980's in Poland under the socialist regime, where homosexuality was socially unacceptable, the protagonist Ludwik (a university graduate) left Poland in 1981 to live in the United States of America. And he remembers what it was like back then in Poland, where he used to hang out with his friends including his first love Beniek in his hometown of Wrocław when he was nine years old. He and Beniek took classes at church for their First Communion, and the day of the First Communion finally arrived.
In this part, I would like to know what "move in" means in this context. Does it perhaps mean that it was difficult to move his body inside the robe...?
I am an English learner from South Korea. I would very much appreciate your help. :)