This answer sounds wrong, but a certain important book tells us it could be right, so bear with me...
I am not lost, but I can be found.
If you have found me, then you should lose me again, in order to find me.
According to the Gospel of Matthew in the Bible, "Whoever finds their life will lose it, and whoever loses their life for my sake will find it."
When you find me again it will surely be of benefit, similar to if you became more fit.
Going with this interpretation, you "find" your life again when you enter Heaven, which is surely a benefit. All your bodily weaknesses will have fallen away, as though you were suddenly more fit.
My composition of attributes is exactly that...
The sum of all your attributes gives your life.
...found of the pages were: on a journey, five had me and five did not.
This could be a reference to the Parable of the Ten Virgins (see the Gospel of Matthew again), in which "five of them were foolish and five were wise). So an alternative possibility would be WISDOM. Thanks to Lawrence for helping me with this line.
And who says I'm rude about Christianity now?!