You raise an excellent point - excellent. I used to run into exactly the same "brick wall" whenever I thought to "teach baptism" - whether to friends, family, etc. And you're right, whenever you attempt to do that, especially with professing Christians, the push-back can be enormous. And you're right again, inasmuch as it usually consists of "whatever their church believes."
I came to the conclusion long ago that baptism is not a topic to be taught - per se. I should explain (definitely, I'm thinking
) - it has been my experience that those who push back as they do with their church's beliefs on the topic are typically not studied themselves in such topics. They know "the basics" and believe in them. When the topic of baptism arises seriously, so too does the question of their salvation - and necessarily so.
To receive a different message about one's salvation would require one to deny what they already believe - in essence, to deny their [current] faith.
This is powerful "push back" indeed. And we should not take it lightly or delve into it hastily (and certainly not without much prayer), nor should we give up either.
When we jump right into a study on baptism with professing Christians, we presume several things that I think may cause the message to be rejected outright. The first is that they know the scripture, and have studied it themselves - as the Bereans did, who searched the scriptures diligently to see whether the things they were being told were in fact true. Many only regurgitate what they're told from the pulpit. Many only study what they're told from the pulpit. Few seriously question however what they're told from the pulpit.
The second thing that we presume is that the person is "ready" to receive such a message. We think that because they are professing Christians, their hearts are eager to know the truth and incorporate it into their lives. To tie that in with what I said above, they may be "eager" to know the truth - as long as the truth is what they already know or believe to be true (or in-line with same) - as taught them by people they have put their faith in to be teaching them accurately. But again, few seriously challenge the veracity of what they've been taught on their own, by studying it themselves with a view to know whether in fact it is true.
Few, for example of such people I've broached this subject with have ever gone back to the bible themselves - they are content to know what they know based on what they've already been told by people they think they can trust (people who frankly may be in the same boat they are in).
I must reiterate, the single greatest "push back" to this particular topic is that it may require some to deny their [current] faith to receive this message.
I believe that, because that was my experience - and a very, very powerful experience it was, let me assure you. I toiled in prayer over this like nothing else I've ever toiled in - scared the living daylights out of me, frankly.
I have but a few suggestions from my own experience - that may or may not be helpful. First - pray and pray consistently and fervently for that person - God will open the right door for you and them in time. Second - earn their trust, not as a friend or co-worker or sibling or son/daughter - but as one who (and who in their judgment) "rightly divides the word" and as one devoted to the word and lives the word. I should point out that the singular most effective thing with me was coming to realize how seriously those who taught me the word took the word. I saw it in everything they did, how the lived, how they fellowshipped, how they worshipped, and how they studied/taught/learned. I'd encountered so many "flakes" of religious types in my journey, everyone was suspect to me - especially "Christians." Third, let them teach you. Be willing to listen and learn yourself. Ask them what they know about the gospel - but keep the scripture as the objective focus of it - not personal beliefs, opinions, etc. - open the word and speak from the word. Study different topics relating to the gospel, faith, sin, repentance, grace, endurance, perseverance, the Word, the church - all with a view to Christ's death, burial, and resurrection - and eventually to how we participate in it.
I'm mindful of Philip and the eunuch - the eunuch who was studying Isaiah and wanted to know about whom was Isaiah talking. ... So Philip, beginning with this passage taught him about Christ - preached the gospel to him. And when taught properly, always generates the same question in the heart of them who have received it properly - "Look! Water! What prevents me...?"
