If you read a thread and disagree with it, I don't get why some pull up the quotes from the original thread and then give their disagreements.
I do this because it helps to clarify what I'm talking about. By quoting this particular part of your post, I'm making it clear that I'm not talking about your stance on religion (I happen to agree with it), and I'm not talking about forgiveness right now (because I've already said what I feel motivated to say).
I also do it at times when someone says something that I regard as particularly noteworthy. If I have questions about what someone has said, then reminding them (and myself, and other readers) of exactly what they said can help remind them of what motivated them to say it.
Why can't you just state your disagreement in your own words.
I suppose that's possible. This way is more convenient.
Rather than picking your post apart one sentence at a time, I suppose I can go on at this point to talk about whether it's 'an attempt to discredit' or not. Cutting things up into little pieces is often used when there is disagreement or puzzlement, or when someone has asked a lot of questions in one post. I can understand that many of us have been 'put under the microscope' by people who did want to discredit us, and that it's an uncomfortable feeling a lot of the time.
Also, don't forget that many of us have difficulties with memory. By picking out a quote, I remind myself of what I'm talking about, and help myself to structure what I have to say.
Also, people tend to remember 'what they intended to say' when they reflect on communications as opposed to 'the words that they actually used'. If someone gets misunderstood or gives offence, it's often because they used words that weren't a very good reflection of what they intended to say. When discussing such a misunderstanding, it can be very useful to remind them of the words that they actually used.