As always, the Ruach Ha'Kadosh should be the one to guide you in all your evangelism, most especially in confrontational open-air evangelism. I have mentioned several places one can preach, but what about churches? Is it ever appropriate to preach in front of a church on a Sunday morning as parishioners are streaming in?
The answer, of course, is yes. Most churches (the proper word is congregations), are extremely steeped in sin. Many so-called Christians are mere pew warmers and sometimes the leadership is not much better. The sin issue does not even begin to address the paganism that has flooded the churches for the past several centuries. There is such a need for modern-day prophets to rebuke, exhort and encourage the churches, trying to get them back on the right track. The real question should be why aren't more believers preaching in front of churches?
The motive to preach in front of a church need not be to reprove of sin. Of course the reaction will generally be negative, but your approach need not be. There is reason enough to preach in front of a church, to encourage and exhort the brethren to good works, evangelism, etc. There is so little being done by modern Christians that, at the very least, a little surprise encouragement couldn't do any harm.
Be prepared for an extremely negative reaction. In preaching in front of churches, you are confronting head-on the religious spirits that control this world. Often times, church members become violent when trying to stop the preacher. The police are almost always called and sometimes jail is threatened. A great deal of prayer will go a long way in helping you soften the stoney hearts of many churchgoers.
Many, even among street preachers, feel that preaching in front of churches is completely inappropriate. But remember, there is biblical precedent. In the Tanach ("Old Testament"), the prophets preached to Israel, who were the religious people of the day. In the Brit Chadasha ("New Testament"), YahShua and Rabbi Shaul preached in the synagogues. Today, the religious crowd could very well be the most ignored and yet the most needful to reach. Most think that those who go to church don't need evangelizing, as they are covered by their pastors. But when we see the extreme amount of wickedness parading through this country, we realize that the pastors and parishioners are not exactly connecting.
If ever revival is going to hit this nation once again, it must start with the cold churches in America breaking their fallow ground and asking YahShua to rain righteousness upon them once more.