What one must note is that the war against Christianity is never always on the obvious. Remember Jesus warned in Matthew 7:14-16 of wolves that come in sheep's clothing. It is a figure of speech that describes the false prophets. They do seem harmless but inside, they are just as dirty as every other lost sinner. There have been many ways Satan infiltrates the church. Paul warns in 2 Corinthians 11:26 and Galatians 2:4 that there is always the peril of false brethren. 2 Corinthians 11:14 warns that Satan can disguise himself as an angel of light. There are many ways he can induce deception that it can deceive Christians for some time. What is worse is that many of these people who teach false doctrines are so blinded to think that they are servants of God when they are ministers of Satan.
The great deception behind Evangelicals and Catholics Together is done in the name of tolerance. When the late John Paul II opened the Mass of Pardon for all the atrocities done in the past, I remembered how many Roman Catholic folks of mine tell me that, "Look you bigot, Pope John Paul II did not even call us to kill you Protestants but it is time to consider you as our brothers and sisters in Christ." Some even raise the late Martin Luther King Jr. and say, "He may have been named after the late Martin Luther but he certainly bridged the gap between Catholics and Protestants." At first, my defenses were down but after reading more of the Roman Catholic institution's history and beliefs especially about salvation, I start to doubt the salvation of pastors who claim to be Christians but embrace Roman Catholics as brothers and sisters in Christ instead of heretics who need to be reached out with the Biblical truth. Even the Jesuit agents are becoming bolder and bolder when they say, "Well Roman Catholics are our brothers and sisters in Christ!"
Another is that an institution may seem Christian because they preach salvation by faith alone and/or go against sinfulness. It is a problem when a Christian may end up thinking that a certain church is a Bible-believing church because they believe in salvation by faith alone in Jesus Christ but surprise, they teach Antinomianism directly or indirectly. I have no reason to believe any pastor is a pastor of God if he preaches eternal security but denies God's life changing grace plus teaching that salvation is a license to sin. Only fake converts would dare embrace such a stupid heresy because those who are truly saved do not want to keep living in sin. One can also preach against sinful activities so fiercely but adds works to staying saved. They can also go as far as to teach that the Biblical truth of the perseverance of the saints is nothing more than a license to sin. Both of them are also very misguided.
The best weapon against infiltration is by being firmly rooted on the Word of God. It is time to really do verse by verse or expository preaching. Enough of taking verses out of context. It is time to do exegesis. More importantly, one must always pray to God for discernment whether or not this person is a brethren or a false brethren that needs to be lovingly confronted with the Word of God. It is not a struggle of flesh and blood but against the demons that control people. Remember even these infiltrators are still given the chance to be saved and they are part of the mission field.
God's Word: Sharper than ANY Deception!