Is performing acts of worship without understanding blameworthy, and does it diminish the reward, or is it considered an imitation of the Messenger, may Allah bless him and grant him peace, in which there is no harm?

Following the Prophet, peace and blessings be upon him, is not mere imitation, because he is the guide upon whom scholars rely, and it is obligatory upon every Muslim. It is not a condition for the validity of following him to know the rulings of the commands or the reasons for their legislation. Rather, hearing and obeying what the Prophet, peace and blessings be upon him, said or did is sufficient, just as the Companions, may Allah be pleased with them, did. While knowing the rulings of the commands and the secrets of legislation has a great effect in solidifying submission, and it is part of seeking beneficial knowledge, the reward does not depend on it. It is not permissible to make submission conditional upon knowing the wisdom.