Why does the congress waste time with the dismissal when the senate will not dismiss it?

This whole masquerade of impeachment has one goal … Democrats are so threatened by Trump's administrative progress that they want it so badly and because they feel they cannot just win and square to the 2020 elections, they are pursuing this simulated impeachment to try to brainwash Americans.

But to answer your question directly, the Congress is involved because it is part of the due process in a dismissal procedure.