Just to add more details. A 1:1 transformer provides so-called galvanic isolation. You can google it. It's a basic feature of basically all modern mains-powered devices, with a little exception of EMI filters in switching-mode PSUs. It turns (either the low-voltage part of, or all of it) the circuit into an IT-type circuit (isolated), which means that enabling the power to merely flow to the ground doesn't enable it to shock you.