I've been reading Van Til's An Introduction To Systematic Theology. Van Til notes systematic theology seeks to offer an ordered presentation of what the Bible teaches about God. He says "the study of systematic theology will help men to preach theologically. It will help to make men proclaim the whole counsel of God. Many ministers never touch the greater part of the wealth of the revelation of God to man contained in Scripture. But systematics helps ministers to preach the whole counsel of God, and thus to make God central in their work."
Here was the point that I found most interesting:
"It is but natural to expect that, if the church is strong because its ministry understands and preaches the whole counsel of God, then the church will be able to protect itself best against false teaching of every sort. Non-indoctrinated Christians will easily fall prey to the peddlers of Russellism, spiritualism and all of the other fifty-seven varieties of heresies with which our country abounds. One-text Christians simply have no weapons of defense against these people. They may be able to quote many Scripture texts which speak, for instance, of eternal punishment, but the Russellite will be able to quote texts which, by the sound of them and taken individually, seem to teach annihilation. The net result is, at best, a loss of spiritual power because of loss of conviction. Many times, such one-text Christians themselves fall prey to the seducers voice."Of course, I had the converts to Roman Catholicism in mind, rather than Russellites. I wonder how many of these Catholic converts actually attended churches that proclaimed the whole council of God? A question I would ask is how many Catholic converts previously went to churches with strong systematic confessions of faith, like the Westminster Confession, and how often were they taught the confession, like in a Sunday School class, and how well did their minister cover all the doctrines in the confession of faith? I would expect some rather weak answers.
Van Til states, "We have already indicated that the best apologetic defense will invariably be made by him who knows the system of truth of Scripture best." I would modify this a bit and make it a negative: "the best converts to false gospels will invariably be made by those who know the system of the truth of Scripture least."
I don't recall writing the above post, but I still find it to be true for a number of garden variety converts. There have been times I've dealt with people who are quite biblically knowledgeable, yet a serious heresy is being entertained. As I've considered what would lead these people to embrace such deviant theological positions, Van Til's words certainly ring true: there was a lack of a strong systematic theology.
There will of course be those that were previously catechized (or even had theological training) who convert to this or that. In fact, now we have the CTC blog which props up people from my own tradition that have made their way across the Tiber. CTC appears to be primarily picking people that were more than simply pew sitters in Reformed churches. As I've read through (or listened to) Roman Catholic conversion stories though, more often than not, one can usually sense a lack of systematic theology.