What are the irreducible elements that make a local church?
Is there ever a time to leave a local church, and what are the criteria?

Recap:

God, is and always has been, forming a people to make himself known. (Week 1: The Church is History)
That ‘people’ is the ekklesia (church), which exists universally and invisibly and is expressed locally and visibly. (Week 2: The Church and A Church)
God cares for these local expressions (churches) through local shepherds. (Week 3: The Church is Led)
Christians are part of a local church to grow in and live out their faith, and to be cared for. (Week 5: What’s a Church Member?”)
1 Peter 1:1-2
The Trinity
God is one but expressed in three persons.

Egg has three distinct parts (shell, yolk, and white) but it is one distinct egg.
Just the yolk is not a complete egg.

Each person of the Trinity is the fullness of God

God has put relationship into His creation because He is relationship.

Excerpt from “What is a healthy church?” by Mark Dever
Before you decide to leave your church:

Pray
Let your current pastor(s) know about your thinking before you move to another church or make your decision to relocate to another city. Ask for their counsel.
Weigh your motives. Is your desire to leave because of sinful, personal conflict or disappointment? If it’s because of doctrinal reasons, are these doctrinal issues significant?
Do everything within your power to reconcile broken relationships.
Be sure to consider all the ‘evidences of grace’ you’ve seen in the church’s life- places where God’s work is evident. If you cannot see any evidences of God’s grace, you might want to examine your own heart once more (Matt 7:3-5).
Be humble. Recognize you don’t have all the facts and assess people and circumstances charitably (give them the benefit of the doubt).
Historical requirements for a local church:

Preaching of God’s Word
Practice of the ordinances (baptism and Lords’ supper)
Irreducible elements of a local church found in 1 Peter 1:22-2:8

The Word is Central (1 Peter 1:23, 25; 2:2)
Jesus is the Cornerstone (1 Peter 2:4-8)
The People are in Process (1 Peter 2:4-5)
Worship is the Point (1 Peter 2:5)