What is the difference between a packer and a bridge plug for downhole operation?

Simply put, in general, the bridge plug is sealed. If a packer is used to seal the layer, it is necessary to add appropriate tools, such as plugs, at the lower end. Personally, I think the packer should go first, and the plug should be used to complete the sealing. Later, the development of bridge plug was equivalent to a tool to combine packer and plug sealing string into one.