Acts 2

(4) All of them were filled with the Holy Spirit and began to speak in other tongues as the Spirit enabled them.
This shows that God's power can achieve what defies human logic or reasoning. He'll use these newfound gifts to speak among the nations.

(38-39) Peter replied, "Repent and be baptised, 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. the promise is for you and your children and for all who are far off-for all whom the Lord our God will call."
Believing in Jesus and acknowledging his sacrifice isn't enough to save us. To not just accept him as our saviour but also as our Lord is what's essential. We have to sacrifice our pagan practices and ideologies to know God on a personal level. This would be difficult for a lot of us as our current culture encourages individuality and to worship ourselves, being our own boss. 

(47) Praising God and enjoying the favour of all the people. And the Lord added to their number daily those who were being saved.
A healthy church will attract potential believers. More often than we should, we gather into our own individual clicks or tolerate sins that makes us feel comfortable or safe. No one would probably have interest in God if his followers don't imitate him. While it is God and not human efforts that provide salvation, we have a responsibility to be used by God.