Thee and thou were once forms of address which were non-formal and intimate, hence the usage in the Bible and in wedding vows, so they would not originally have been used to denote respect to, say, strangers. However, they came to be used in literary works to indicate that the speaker is ill-educated and doesn't know when to use the correct form for the social situation; they are "overly-familiar", often due to being good-natured. This latter is probably the intent for at least some of the uses in Uncle Tom's Cabin.
The words can also be used in an insulting way, to suggest that the object is not worth a formal address.
As the words fell out of usage they became associated with old-fashioned speech and, as often happens, old-fashioned speech was itself associated with stiffness and formality. So a modern native English speaker will often have exactly the opposite understanding to the correct one - that "thee" and "thou" are especially formal instead of being friendly or relaxed pronouns for use in private situations with friends, children, and lovers.
A final complication is that regional (that is, English spoken in different parts of the UK) English contains these words even today but in my experience they are mostly used in the belittling/insulting manner but with an undertone of jokiness or teasing.
It used to be... but it's no longer used in everyday speech... actually, I don't think it's used outside of Renaissance Festivals and old plays any more... maybe LARPing? – Catija – 2015-04-05T05:31:12.197
1Thee is the direct object or objective form of thou, which used to be the second person singular pronoun. (With this ring I thee wed.) We now use you for both singular and plural. While thou can still be found in some rare places like book titles, thee is now even more rare and probably found mostly in old forms of prayers: We thank Thee, O God, for... In this sense it is more respectful, but only because of the direct object. – None – 2015-04-05T05:43:07.620
@δοῦλος Thanks for your comments, interestingly enough google says that it’s been used more and more since 1995, at least in written english.
– rraallvv – 2015-04-05T05:47:49.7105
You can't really just look at it in a vacuum like that... the numbers there are pitifully small and you're looking at written works, not spoken... which just means people are writing more period novels. It doesn't mean it's used in modern... see it compared to you.
– Catija – 2015-04-05T05:53:03.8072Even more surprisingly, I added you to that Ngram chart, and found that you has been steadily increasingly used since 1966! (PS. Please don't take this message seriously. :-) – Damkerng T. – 2015-04-05T05:55:35.110
2I should add that thee is also for indirect object. As far as a trend upward in usage, if that is true, meh, it's when people want to sound a bit different, because they lack imagination. The word is certainly not going to come back into everyday use! – None – 2015-04-05T05:56:16.133
1It's been in everyday use in Northern UK since time immemorial, though in speech it's now been reduced to an almost generic "tha" or "thi" sound replacing thee thou or thy. "Tha'll attu get thi booits on before tha go's out in't rain, lad!" (Wow, that was a fight against auto-correct ;-) – gone fishin' again. – 2015-04-05T10:52:17.157
1Traditionalist members of the religious Society of Friends (sometimes called Quakers) also use thou/thee. But in modern mainstream English you has supplanted these forms. – Tᴚoɯɐuo – 2015-04-05T16:39:49.157
It was more formal, but was not necessarily more respectful. As @Catija points out, it's simply no longer used except in highly-specific vernaculars. – Superstringcheese – 2015-04-05T18:23:06.280
"thee" is and old way of saying "you". It is almost never used in modern english. – Jojodmo – 2015-04-05T22:47:34.620
@Superstringcheese: Indeed, since thou is the familiar form, in many cases it was less respectful. In Shakespeare you generally see people addressing their superiors as you and their inferiors (or superiors whom they wish to insult) as thou. – Nate Eldredge – 2015-04-06T03:12:56.017
The reason why some Quakers still refer to each other as thee is because they refuse to recognize worldly distinctions between men (no "hat honour"). – J. LS – 2015-04-06T12:03:03.957
Long term, learning a language from grammar books and a dictionary is the greatest disservice you can inflict on yourself. Even basic grammar books contain constructs that are never used and ones that are used every day, with no indication to the learner which is which. As soon as possible you should switch to learning 80% to 90% by usage, or at least by just listening to the language. You would know then that thee is never used these days. – None – 2015-04-05T15:54:47.837