I often notice many "Christians" say things like "Jesus only taught one thing" or "Jesus only taught two things", when I see that I often have to wonder if they missed all the hundreds of specific teachings that Jesus taught.
It's possible that you misunderstand what someone means when they say this.
If you look at hebraic law (which preceeded Jesus) there are
hundreds of different instructions to follow. (I forget the exact number, but I vaguely recall it being between 600 and 800 different laws, excluding duplicates.)
However, the jewish sage Hillel the elder was once challenged to recite the entire law while standing on one foot. In response, he said:
"That which is hateful to you, do not do to your fellow. That is the whole Torah; the rest is the explanation; go and learn."
In the same manner, I could claim that the only thing Jesus taught was the great commandment. For example, the golden rule (Do unto others as you would have them do unto you) is an explanation of how to "love others as you love yourself."
Hillel did not see the Torah as containing hundreds of laws. He saw it containing
one law, and hundreds of explanations. Similarly, it's possible that the christians you hear aren't ignorant of what Jesus said. They just see most of it as examples which explain one teaching.
Have you read the entire Bible?
I've read the entire new testament, and the majority of the old testament.
Do you think you personally know enough about what it says to be able to make claims about it?
Depends on the claim. My memory is not perfect. My understanding of the context the bible was written in (the society it was written in, the history of the author, the intended audience) is limited.
If your knowledge of the Bible comes from cherry picked verses, have you considered reading the entirety of the text, and do you think such would be a valid investment of your time?
It depends on my goals. I found a couple chapters to be wonderful cures for insomnia. However, if my goal is to learn how to treat people better, I don't think I really need to know the proper way to consecrate a temple or sacrifice a lamb.
Do you think a "Christian" should read the Gospels before discussing them, let alone the rest of the Bible?
In your classes in school, did you have to read the
entire textbook before the first discussion group? Did you even have to read the
entire textbook before the final exam?
I recommend that people learn about their beliefs. I think they'll learn faster if they engage in discussions
during the learning process.
Do you think Christians should NOT attempt to discuss doctrine and Theology if they don't have a sufficient grasp of what the text even says?
Do you ever discuss matters of personal health? If so, when did you get your medical degree?
I'd actually lean the other way. People should begin participating in discussions even at the very beginning of the learning process.
Or do you think knowledge of a few key verses is sufficient?
I think knowledge of a few key verses is
crucial.
I see too many christians cherry-picking verses that serve their own biases without acknowledging that those verses should
only be examined in relation to the most important teachings (the great commandment, the golden rule, the love chapter).