The first words in our sedra are instructions from HaShem to Moshe ‘and you, command Bnei Yisrael…’ But Moshe has been conveying instructions regarding the Mishkan construction thus far anyway – so why does HaShem need to repeat ‘you, command the Bnei Yisrael?’ The Rashbam writes that this portion is dealing with the making of the oil for the ner tamid – which is an instruction for each generation to bring the ingredients, whereas previous instructions to the Bnei Yisrael were one-off instructions vis-à-vis the structure of the Mishkan. That is why these instructions are different and deserve their own separate introduction/calling. Others stress the word ‘you’ to mean that Moshe must personally instruct the Bnei Yisrael here, as opposed to instructing the craftsmen only (Sforno).