"How, then, can they call on the one they have not believed in? And how can they believe in the one of whom they have not heard? And how can they hear without someone preaching to them?" Romans 10:14
Some people get frustrated with God because they feel like God isn't answering their prayers. Sometimes it takes time. But sometimes it's because of our own sins. Nonbelievers can't pray to a God who they don't even believe in and expect Him to answer their prayers. Although they might claim they are Christians, how does their life reflect upon Jesus? Therefore we need to intercede for those who don't know Him. Pray for our church members, for our small group members, for our friends who aren't Christians.