J. B. Heaton & J. P. Stocks say in their OVERSEAS STUDENTS' COMPANION TO ENGLISH STUDIES (LONGMANS, 1966) that we seldom use 'can know':
We can know all about India in our geography lessons. (wrong)
We should say: We learn all about India in our geography lessons.
I don't know why 'can know' is wrong. Here are a few sentences from the Internet. Could you tell me whether they are wrong too and why?
Thank you very much in advance.
1. Christ said that He would come into your life and be your friend so you can know him personally.
2. Through Him you can know and experience God's love and plan for your life.
3. Good! At least we can know what he has done this while.
Heaton and Stocks say that "can know" is seldom used, which means that sometimes it's possible.
A sentence like "We can know all about India in our geography lesson" sounds unnatural because we never normally have to express the idea that somebody has the ability to possess information about India. Either you know about India, or you don't. What is needed here is a more active verb, like "learn": "We can learn about..." means we have the opportunity to find out about India, and that's more useful.
The three sentences you have found are rather different. I'm not sure the 3rd sentence was written by a native speaker, though, as it sounds very unnatural to me.
But in sentences 1 and 2, "know" has a different meaning: it means "become acquainted with" or "experience"; and "can" in each case means "have the opportunity to". This construction is a little old-fashioned, and so you'll often see it, as here, in religious contexts.