Why didn't congress have the power to tax

Congress is authorized to lay and collect taxes, etc., to pay the debts, and provide for the common defense and general welfare of the United States. Then, each government exercises the power of taxation, neither is exercising the power of the other." While authorizing Congress to levy taxes, this clause permits the levying of taxes for two purposes only: to pay the debts of the United States and to provide for the common defense and general welfare of the United States.