Привет. За основние исправления; и за cтильные улучшения -

Our purpose

Hi. I guess we are here not so just. I guess we are not here, "just so". I suppose we are not here just for the sake of it./ I guess we are not here for no reason.

We have (a) purpose. Our the most important task in the life is found our purpose. Our the most important task in the life is to find our purpose.

But after we must do what we have to. But for that, we must do what(ever) we have to. [Я не совсем уверен, может быть: But other than that, we must do what(ever) we have to...] 

Sometimes for this task need 20 years, but sometimes we haven't to do it for all life. Sometimes this task needs/requires/takes 20 years, but sometimes we don't succeed in it/achieve it for all our lives/ ...but sometimes a lifetime is not enough.

We will not forget that we can change everything and we must do it. We must/should not forget that we can change everything and we must (be prepared to) do it.

Your life is the most important life. Don't lost your time Dont lose any time. / Don't waste your time. / Don't waste any time.

Good work here. Posts/Entries with a little meaning, about ideas, are enjoyable to read.