Question: For the sake of argument, let's say I'm a Roman Catholic who is prepared to renounce the Church. Please tell me, which Protestant church should I join? After all this time being in a "false religion," I am ready for the complete truth untainted by error, and will settle for nothing less. Please tell me how I can determine with absolute certainty in which church I will find the fullness of Christian truth, since there are many dozens of large denominations, hundreds of smaller ones, and thousands of independent churches, all teaching differing and often contradictory versions of "sound, Biblical doctrine" on critically important doctrinal issues which relate to salvation.
Response:I can't tell if you are really a Roman Catholic or someone who is truly interested in and seeking the truth. I'm guessing the former but hoping the latter (which is why I'm taking the time to respond).
First of all, no one is saved by belonging to a denomination or church, whether Baptist, Episcopal, Methodist, Catholic, Orthodox, or whatever. Salvation is neither a group plan nor a "membership thing." Everyone is personally accountable for his every belief, thought, word, or deed, before the Lord. Everyone stands alone before God in judgment, with no board of elders or magisterium backing him up.
So, whatever church a person attends is only worthwhile to the degree that it helps him to know, believe, and live out the truth of the gospel. Jesus prayed for those who would believe in Him, "Sanctify them through thy truth: thy word is truth" (Jn:17:17). Only God's Word, therefore, is where the "fullness of Christian truth" is found with "absolute certainty."
"Christian" churches can range from being wonderful blessings to being cults; their conformity to the Scriptures is the deciding factor. Who decides? Anyone who can read the Scriptures and compare what a church teaches and practices with what the Bible says (Acts:17:10-11)! That's the same "anyone" who will stand by himself or herself in judgment before the Lord. When Jesus addressed the seven churches (Rv 2,3) that are representative of churches throughout history, there was only one He did not correct: the church at Philadelphia. All the others (except for Laodicea) had some good points, but then some bad points that needed to be corrected.
If you are actually serious about joining a church, it would be great if you could find a "Philadelphia" type church-one that Jesus could commend fully because it was true to His Word. That not being the case, it is hoped that you would choose a church that preaches the biblical gospel, looks to the Bible as its absolute authority, and is open to being corrected by it. Those three points, by the way, disqualify the Roman Catholic Church as an option.