As a consequence, I asked how God can forgive everyone, because some misdeeds don't seem forgivable for me; and if everything is forgivable, then I might as well be sinful and have a lot of fun before I come into paradise. My friend agreed with me, but said that we should still try and be good, because he don't want to let his parents suffer by harming other people.
I had some further reactions to your story, and I want to point out that...I think it is important to be careful about the word "sin" (and "sinful") because there are two things being mixed up here.
One understanding of "sin" is that it is the harming or hurting of another person, and all the things that we in a civilized world, understand as "wrong" because they cause pain to someone else. There are different levels of moral understanding: It could be based on fear of punishment - either by the judicial system of society, or by social ostracisation (or fear of getting a bad reputation or disappointing others). Also most people will react toward inflicted pain with some kind of retaliation, or they will no longer trust you. We also have our inner conscience and this will follow us for the rest of our lives in the form of our memories. When you fully understand "pain and pleasure" you see the importance of non-harming. Every person moves toward pleasure and recoils from pain. Why would you do to someone something that you would not want to be done to you? If you cause pain to others, and then justify it in some way, you will begin to attract others to you who also cause pain to others...and this will put you into harms way...and then you will live in fear that you will be harmed.
Then secondly there are the "sinful" things which have been invented to "try" to make certain aspects of civilization function more smoothly, but come from some religious opinions (for example: sex before is wrong marriage, dancing is wrong, drinking alcohol is wrong, etc.) and these opinions are not inherently correct. These are things which only cause pain when there is a lack of mutual consent or when there is over-indulgence (when there is a potential for pain, and when the person is not being fully responsible). So would guess it this second instance of "sinful" in which you said "might as well be sinful and have a lot of fun".
And I want to correct this idea of "sin" being "fun"...as this is incorrect. We cannot live a joyous life without living wisely and rightly:
Principle Doctrine 5:
5. | It is not possible to live joyously without also living wisely and beautifully and rightly, nor to live wisely and beautifully and rightly without living joyously; and whoever lacks this cannot live joyously. [note] |
Also there is this with regard to the second category I wrote about, and so one makes choices not to do things that will result in pain. For example, I would say that at all Epicureans would not do binge drinking.
8. | No pleasure is bad in itself; but the means of paying for some pleasures bring with them disturbances many times greater than the pleasures themselves. [note] |