EtherChannel is a link aggregation protocol designed to run with STP to allow line groups intended to increase bandwidth to act as a single Link
If you need more bandwidth between devices multiple links (wires) could be connected between devices to increase bandwidth
However, Spanning Tree Protocol will block redundant links to prevent switching loops
This is why EtherChannel is Needed
Redundancy
Loop Avoidance
Link Aggregation
These concepts are building on each other