The local church is the physical representation of the larger body of Christ in a particular place at a particular time. It is the nexus of the Christian life; the place where the means of grace for sanctification are found. God's design for His people is that we do life together, and we can't be fully obedient to Him unless we're connected with His people. Church discipline is one of the means of grace He has provided for the preservation of His people and the purity of His church, and it is one of the corporate duties we fulfil in the context of our commitment to one another.
The church of Jesus Christ is commanded to take sin seriously because we are called to be holy. We do this by covenanting together in a local church and committing to following our Lord's instructions concerning how to deal with sin within the context of that community. Christ has provided a universal, step-by-step set of instructions for how to do this which is commonly referred to as church discipline. When we embrace these divine directions in obedience and seek to rightly understand and apply them, we will find that discipline is a means of grace for His church.