In the universal church as the Body of Christ, made up of those who believe in God as revealed it the Scriptures and who unite for worship and service. Each believer, born of the Spirit, is an integral part of the Church. Since God’s purpose concerning man is to seek and to save that which is lost, to be worshipped by man, and to build a body of believers in the image of His Son, the primary reason-for-being is:

a) To be an agency of God for evangelizing the world.
Acts 1:8
"But you will receive power when the Holy Spirit comes on you; and you will be my witnesses in Jerusalem, and in all Judea and Samaria, and to the ends of the earth."

Matthew 28:19-20
"Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, and teaching them to obey everything I have commanded you. And surely I am with you always, to the very end of the age."

Mark 16:15-16
He said to them, "Go into all the world and preach the good news to all creation. Whoever believes and is baptized will be saved, but whoever does not believe will be condemned."

b) To be a corporate body in which man may worship God.
I Corinthians 12:13
For we were all baptized by one Spirit into one body—whether Jews or Greeks, slave or free—and we were all given the one Spirit to drink.

c) To be a channel of God’s purpose to build a body of saints being perfected in the image of His Son.
Ephesians 4:11-16
It was he who gave some to be apostles, some to be prophets, some to be evangelists, and some to be pastors and teachers, to prepare God's people for works of service, so that the body of Christ may be built up until we all reach unity in the faith and in the knowledge of the Son of God and become mature, attaining to the whole measure of the fullness of Christ. Then we will no longer be infants, tossed back and forth by the waves, and blown here and there by every wind of teaching and by the cunning and craftiness of men in their deceitful scheming. Instead, speaking the truth in love, we will in all things grow up into him who is the Head, that is, Christ. From him the whole body, joined and held together by every supporting ligament, grows and builds itself up in love, as each part does its work.

I Corinthians 12:28
And in the church God has appointed first of all apostles, second prophets, third teachers, then workers of miracles, also those having gifts of healing, those able to help others, those with gifts of administration, and those speaking in different kinds of tongues.

I Corinthians 14:12
So it is with you. Since you are eager to have spiritual gifts, try to excel in gifts that build up the church.