Well you need to learn life lessons to get you through life. Not to use after death. I've learned lots of lessons the hard way but at least I won't make them again (hopefully). Learning and growing is just a process that makes life easier.
There is so much that I want to learn, for me, to know in this life. Of course it all seems like a waste, since it won't do me any good after I die, but this just isn't so. I love learning new stuff, it makes me happy. Happiness in the end is it's own reward. I fully expect to be on my deathbed, asking questions of the doctors about things that have nothing to do with my condition, and of my loved ones about things they have been up to in their own life. I will probably forego asking any clergy questions, as so few of them have anything in the way of facts.
You might as well ask why we need to know anything if we just die. Uh, maybe because we have to live and it will be more pleasant and rewarding if we actually learn something along the way. Whether there is an afterlife is irrelevant as far I can see.
Do you really believe this life is all there is? I left a religion for teaching that, because that mentality led me to being suicidal for 15 our of 18 years of my young life.
You're right, there is so much to learn. How could you learn it in one life time?
So... the LDS church way is out since it was written on lies and stories.
There is the option of believing in reincarnation - we keep going and each new life lets us fix and learn from past mistakes and gives us the option to literally try a different set of circumstances... (One life boy, one life girl, one life rich, one life poor, different races each time, etc.)
On a spiritual scale, if the universe is all about progression and learning love and understanding, it's a great way to do it as a soul along with retaining and learning new things each time. It is also a way to truly learn the ultimate compassion for all people. (when you experience something- it's the ultimate teacher).
I think of the earth as a kindergarten planet. Before we more on , we have a lot to learn here first. (It's sad that after about 6,000 years of written earth history - people still have to be told not to lie, cheat, steal or murder). Perhaps as we get these right, we'll get to move on.
I don't think we're here to learn lessons. As others have mentioned, you just tend to learn them along the way anyway. You make mistakes and then think to yourself, "Well that didn't go well. I won't make that mistake again."
It does help you get along better in the society that you live in. If you've made a dumb mistake like texting and nearly getting hit by a car, it helps you to stop and pay attention when you cross the street, so that you don't accidently cut your life short.
Your lessons help you here, not necessarily in some unknown invisible place.
A lesson might take the form of learning to wear sunscreen after a miserable sunburn, or learning that I feel so much better and I get more done if I exercise in the morning. Maybe I learn to keep my mouth shut instead of spouting off about someone else. Hopefully, all the little lessons add up to learning to live well.
I think it's key, though, not to think of life as a TEST. Nope, not a test. It's the real deal. The one and only chance to live.