Section 12. The creation of the authority is in all respects for the benefit of the people of the commonwealth and for the improvement of their health, safety, welfare, comfort and security, and its purposes are public purposes and the authority will be performing an essential governmental function. The commonwealth covenants with the purchasers and all subsequent holders and transferees of the notes and bonds issued by the authority, in consideration of the acceptance of any payment for the notes and bonds, that the notes and bonds of the authority, issued pursuant to this act and the income therefrom shall at all times be free from taxation.