Why do Christians appeal to personal gain and inducing fear when attempting to "convert" people? I have many times witnessed christians trying to convince or convert atheists or people of other religions to christianity as well as all sorts of arguments and quarrels regarding christianity. I'm sure you've witnessed some too...

Among other things, I've noticed christians persistently using two arguments that I find hard to reconcile with the rest of Christianity / Jesus' teachings:

Appeal to personal Gain

I'm sure you've heard someone say "Start believing in God and Jesus Christ, that way you will be saved and after death you'll go to heaven and be happy for eternity".

Sounds great, the trouble is, if this becomes the sole or main reason for faith, is that faith really worthwile? It seems to me that this argument reduces christianity to a simple trade: Do something that is asked of you and in reward you will be happy forever. I'd think that a real faith would be based on something more... sincere.

I don't understand how can someone venerate Jesus for his act of ultimate selflessnes and love (the crucifixion) but at the same time try to lead people to Jesus by appealing to their desire for personal gain.

Inducing fear

A.k.a. the age-old "If you don't listen, you will go to hell". This is similar, usually used along with the former argument, but it's a bit more drastic. My concern about this argument is essentially the same: If someone believes simply because they want to avoid hell, is that a sincere faith?

It troubles me even more considering that Jesus himself used this argument, although perhaps in somewhat less threatning way (The weeping and gnashing of teeth, "Fear that who kills the soul in hell").

I've heard people say that fear of God is a "good kind of fear", referring to a couple of verses in the Old Testament, but that doesn't really help since fear of God isn't necessarily the same as fear of hell (or is it?) and also (in my experience, anyway) fear is an obstacle to faith or love, that works against them. How could I possibly truly love God while having fear he might as well let me burn in hell? I don't think I could.

Why are these arguments used? 

Are they valid or do people use them just to draw attention to themselves?
These two lines of reasoning are, as you've presented them, problematic as you suggest. Ideally, they'd be used together and be founded in the true message of the gospel. 

First, the few details to be cleared up: 


  I don't understand how can someone venerate Jesus for his act of ultimate selflessnes and love (the crucifixion) but at the same time try to lead people to Jesus by appealling to their desire for personal gain.


Good point. Firstly, though, personal gain isn't bad. It's great. We're wired to want the best for ourselves - and God's given us plenty of things to enjoy. Personal gain and selflessness are not necessarily mutually exclusive - however, in this fallen world, we often must sacrifice personal gain in order to show selflessness. Secondly, there is no comparison between the earthly gain we sacrifice and the heavenly joy we inherit. The latter is so great, so wonderful, that we should want to do anything to attain it. Additionally, keep in mind that the default state of mankind before sin was to be in the presence of God. Made in the image of God, we want to get back to that state, but we can't. Faith in Christ offers us a chance to do that.

Of course, you're right - both of these reasons are alone insufficient, and lack the true message. That message is this: that despite our sinful state before God that should place us in hell according to his justice (appeal to fear), God has sent his Son to die for us and give us the inheritance of Christ and eternity with him. (appeal to joy)

So the real reason anyone should want this faith is out of gratitude - sheer gratitude. Even if God had simply saved us from Hell, but not given us anything else, we'd be so eternally grateful because Hell is so eternally terrible that we'd want to give him everything. But he's not only given us mercy, but grace, so our gratitude abounds, and our faith is sincere.