Repent and be baptized, every one of you, in the name of Jesus Christ for the forgiveness of your sins

Acts 2:37-47
When the people heard this, they were cut to the heart and said to Peter and the other apostles, "Brothers, what shall we do?"
Peter replied, "Repent and be baptized, every one of you, in the name of Jesus Christ for the forgiveness of your sins. And you will receive the gift of the Holy Spirit.
 With many other words he warned them; and he pleaded with them, “Save yourselves from this corrupt generation.” Those who accepted his message were baptized, and about three thousand were added to their number that day.
 They devoted themselves to the apostles’ teaching and to fellowship, to the breaking of bread and to prayer.  All the believers were together and had everything in common. Every day they continued to meet together in the temple courts. They broke bread in their homes and ate together with glad and sincere hearts, praising God and enjoying the favor of all the people. 
And the Lord added to their number daily those who were being saved.
God is calling to himself. The baptism of 3000 people is followed by a new, joyous sense of community. This finds practical expression in a readiness to share money and possessions. It is sustained by a new pattern of life.
Why?
They were cut to the heart for Peter said the grace of Jesus Christ and God's plan. So they were return to the Lord, and said what shall we do?
The only way to save their life is "Repent and be baptized in the name of Jesus Christ for the forgiveness of your sins.
Away from this corrupt generation, the world is attractive the Christian have to isolate ourselves from the world, even we are living in the world.
There were the church life in the first generation. They devoted themselves to the apostle's teaching and to fellowship...
when there is the Holy Spirit ,the number of church is the Lord added to church.
How?
Be humble and let church be filled with God's word and Holy Spirit.