It is not a command. It is simply instructions as to what they are to do after Jesus ascended.
otherwise they will stand there twiddling their thumbs.
If people would think about it. They lived with him, followed him for 3.5 years, then he died for no reason.
He was resurrected. They thought that meant that he would restore Jerusalem to Israel rule. He said no. They wondered, what next.
He said to go teaching of him and the kingdom. He knew they had to wait until 1881 revolutions of the earth around the sun until the kingdom would be established and that would occupy them.