Below, Tim Keller has some great thoughts on the early church and how fellowship and community was a springboard to outreach and evangelism.
Fellowship & Community Fellowship was intense ("they devoted themselves ... to fellowship" v. 42). It was therefore not something that just happened. They worked at it. This implies accountability with one another, a sense of responsibility to care and support and guide each other. It was daily ("every day "v. 46). They did not just see each other on Sundays, but were involved in each other's daily lives. It was economic as well as spiritual ("had everything in common "v. 44). They recognized not only that other brothers and sisters had a claim on their time and heart but also on their resources.
It was very small group/house church based, "they broke bread in their homes" v. 46. This statement as well as the one found in Acts 20:20, "teaching you in public and from house to house" and greetings to "the church that meets in their house" in I Cor. 16:9 and elsewhere-we can see the importance of small group community in the early church. They had regular meetings where this same set of ministries--learning, loving, worshipping--was conducted at the mini-level, so as to supplement what was happening at the "maxi" large group level. Their fellowship and community was extremely sensitive. They knew immediately who had "need" (v.44).
Outreach & Evangelism The outreach and evangelism was dynamic. They experienced conversions "daily "v. 47. Their outreach was based on demonstration through community. One reason that people were saved is that the love and note of praising was highly attractive to "all the people" (v. 47). This cannot mean that every non-Christian loved the early church because there was certainly plenty of persecution. But it meant that overall the early church demonstrated the gospel in its community in such a way that was irresistible to outside observers.
- Read the rest of Keller's thoughts on Clarifying the Purposes for the Church