It is hereby determined that the creation of the agency is in all respects for the benefit of the people of the Commonwealth, for the improvement of their health and welfare, and for the promotion of the economy, and that such purposes are public purposes and the agency will be performing an essential governmental function in the exercise of the powers conferred upon it by this act, and the Commonwealth covenants with the purchasers and all subsequent holders and transferees of bonds, notes and other obligations that the bonds, notes and other obligations of the agency issued pursuant to this act and the income therefrom shall at all times be free from taxation, except for estate or gift taxes and taxes on transfers.