They are practicing to reach an understanding of the 4 noble truths.
The truth of suffering
The truth of the cause of suffering.
The truth of the cessation of suffering.
The truth of the path leading to the cessation of suffering.

According to the Theravadan perception this is all the Buddha himself said he taught.
He sometimes elaborated on the nature of the Tathagatha, but only if such an explanation would help someone understand the 4 noble truths.

He didn't teach enlightenment. Nor spirituality.. Just these four noble truths

With Love
Eelco