There is some awe mixed with the joy of our surprise, when this poet, who lived in some past world, two or three hundred years ago, says that which lies close to my own soul, that which I also had wellnigh thought and said. But for the evidence thence afforded to the philosophical doctrine of the identity of all minds, we should suppose some preestablished harmony, some foresight of souls that were to be, and some preparation of stores for their future wants, like the fact observed in insects, who lay up food before death for the young grub they shall never see.

But for the evidence: Except for the evidence, If the evidence would not exist

some foresight of souls that were to be: some anticipation of the souls [new generations] which were to come/appear

The rest is up to you.
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No, I edited my translation, I think it's more correct and clear now.
I won't explain the rest. Takes too much time.
stores for their future wants: reserves/provisions for their future needs
Bulk translation:

We rediscover thoughs which others had before us, 2-300 years ago.
It's as if/though they prepared provisions/reserves (of thought(s)) for us, the current generations.
Students: Are you brave enough to let our tutors analyse your pronunciation?
Thanks a lot, Marius !!

I will give it some thought to find out the meaning.....