It is not about the page actually but the transmission protection.

Which also means that when you are not using HTTPS or you have HTTPS error, then your data will not be encrypted when sending out to the server. It will be something like you are shouting your username and password along a hallway where if people happen to tap your connection, they will see everything.

HTTPS will be like whispering to the server. It is encrypted and your username and password will probably look like this:
5ASDBUIH28HFA9HF380F90FJQ309FJ09FJ09J1Q309...

Sorry for the bad example but final say, don't do your online banking if you are not having a proper HTTPS connection.