Colossians 1:24
I now rejoice in my sufferings for you, and fill up in my flesh what is lacking in the afflictions of Christ, for the sake of His body, which is the church. NKJV
Christ' body is the church. The church is not a building nor is it any particular denomination. The church is made of people all over the world who have discovered the love of God as demonstrated by Jesus Christ.
The following scripture from Ephesians makes it abundantly clear how we become part of the body of Christ; also known as the household of God
Ephesians 2:13-22
13 But now in Christ Jesus you who once were far away have been brought near through the blood of Christ.14 For he himself is our peace, who has made the two one and has destroyed the barrier, the dividing wall of hostility,
15 by abolishing in his flesh the law with its commandments and regulations. His purpose was to create in himself one new man out of the two, thus making peace,
16 and in this one body to reconcile both of them to God through the cross, by which he put to death their hostility.
17 He came and preached peace to you who were far away and peace to those who were near. 18 For through him we both have access to the Father by one Spirit.
19 Consequently, you are no longer foreigners and aliens, but fellow citizens with God's people and members of God's household, 20 built on the foundation of the apostles and prophets, with Christ Jesus himself as the chief cornerstone.
21 In him the whole building is joined together and rises to become a holy temple in the Lord. 22 And in him you too are being built together to become a dwelling in which God lives by his Spirit. NIV
Faith in the shed blood of Jesus brings a person into the household of God. We have access to God through Jesus. Repenting and forsaking of sin can only take place when we accept that Jesus died to pay the price for our peace with God.
The church is the body of Christ. A body is a living organism. Just like our physical bodies are made up of different parts such as hands, legs, ears and eyes. So is the body of Christ made up of different parts.
Each part is essential to the proper functioning and growth of the body. Our stomachs are essential to our well being.
They may not be prominent, and much of the work they do is not always obvious, yet few of us would doubt their importance.
Each person is important in the body of Christ. We all need to play our roles no matter how insignificant they may appear. Those singing, those praying, those ushering and so on, all are playing vital roles.
Each local church or Christian fellowship is part of the body of Christ. Our individual roles within the local church are God given and important.
Only heaven will reveal how many churches have failed because somebody who was planted in the church to play the role of an encourager, neglected their role, considering it too small or unimportant and walked away.
This is true of many different roles that God has given to individuals. Roles that have not been fulfilled.
The following scripture shed more light on our roles as individuals in the body of Christ
1 Corinthians 12:12-28
12 For as the body is one and has many members, but all the members of that one body, being many, are one body, so also is Christ. 13 For by one Spirit we were all baptized into one body--whether Jews or Greeks, whether slaves or free--and have all been made to drink into one Spirit.14 For in fact the body is not one member but many. 15 If the foot should say, "Because I am not a hand, I am not of the body," is it therefore not of the body?
16 And if the ear should say, "Because I am not an eye, I am not of the body," is it therefore not of the body? 17 If the whole body were an eye, where would be the hearing? If the whole were hearing, where would be the smelling?
18 But now God has set the members, each one of them, in the body just as He pleased. 19 And if they were all one member, where would the body be?
20 But now indeed there are many members, yet one body. 21 And the eye cannot say to the hand, "I have no need of you"; nor again the head to the feet, "I have no need of you."
22 No, much rather, those members of the body which seem to be weaker are necessary. 23 And those members of the body which we think to be less honorable, on these we bestow greater honor; and our unpresentable parts have greater modesty,
24 but our presentable parts have no need. But God composed the body, having given greater honor to that part which lacks it, 25 that there should be no schism in the body, but that the members should have the same care for one another.
26 And if one member suffers, all the members suffer with it; or if one member is honored, all the members rejoice with it. 27 Now you are the body of Christ, and members individually. NKJV
Acts 2:40-47
40 And with many other words he testified and exhorted them, saying, "Be saved from this perverse generation." 41 Then those who gladly received his word were baptized; and that day about three thousand souls were added to them.42 And they continued steadfastly in the apostles' doctrine and fellowship, in the breaking of bread, and in prayers. 43 Then fear came upon every soul, and many wonders and signs were done through the apostles.
44 Now all who believed were together, and had all things in common, 45 and sold their possessions and goods, and divided them among all, as anyone had need.
46 So continuing daily with one accord in the temple, and breaking bread from house to house, they ate their food with gladness and simplicity of heart,
47 praising God and having favor with all the people. And the Lord added to the church daily those who were being saved.
NKJV
The church is a body. It is supposed to grow like our physical bodies. Growth in the body of Christ should be in three vital areas
Physically - a numerical growth, with people getting saved (Acts 2: 40-41)
Spiritually - a greater awareness and understanding of the all-powerful God we serve. A greater love for God and a desire to serve Him sacrificially is evidence of spiritual growth. Spiritual growth precedes physical growth. Spiritual growth affects our heart and attitude to the God we serve. (Acts 2: 43 - 47)
Mental growth - a clearer understanding of the teachings of Jesus. This is essential if we are to witness unity in the church. It will also help us in presenting the gospel to the world. (Acts 2:42-44)
You should have noticed that the three areas of growth mentioned above are similar to those required by our physical bodies. This should be no surprise since the church of God is also a body.
How often have we ignorantly measured the growth of a local church by only one of the above criteria? Concentrating on only one of the areas mentioned above can lead to error. Church history is full of testimonies to this.