Remember that the church is God's house. God planned the church centuries before it began. C. Jesus Promised to Build It. People put great effort into planning something only if it is important to them. If they consider their wedding ceremony to be important, a bride and groom make many plans.
Auto makers spend much time and effort in planning new models.
So Jesus put much effort into planning the church. Clearly it was important to Him. God's plan was a plan to save men from sin, and Jesus came to work that plan. The church is an essential part of that plan. Therefore, the church is essential to our salvation.