Thee point is . . .

Q. In church, the words thee, thou, thy, and thine show up in hymns, but nobody uses them in real life. Why is that?

A. Once upon a time--thanks to Scandinavian contributions to Germanic Old English--our pronoun system was very complicated. A strange feature of language is that, unlike government, it gets simpler as it ages.

The words you mention, along with others, were forms of what is called the second person pronoun (the one spoken to). Thee, thou, thy, and thine were used to speak directly to an individual in an intimate way. You and ye were used to address a group.

Each function of a pronoun--singular, plural, subject, object, modifier--had its own distinct spelling. In the second person, we are now reduced to you (the only spelling for singular, plural, subject, object), your (modifier right in front of the word it modifies), and yours (modifier at a distance from the word it modifies).
You dislike Tom.
Tom dislikes you.
Your dislike is apparent.
The loss is yours.

Thou used to be the singular subject form (Thou hearest my prayers) and thee was the singular object form (We beseech Thee, hear us). Thy was the singular modifier to use right in front of the word modified (Thy kingdom come) and thine was the singular modifier placed at a distance from the word it modified (For thine is the kingdom and the power and the glory).

We find an example in the King James Version of the Bible. In the 5th chapter of Luke, we encounter the story of the man with palsy who is brought before Jesus for a cure; his friends let him down through the roof because things are so crowded. In the 24th verse, we find this: “But that ye may know that the Son of man hath power upon earth to forgive sins, (he said unto the sick of the palsy), I say unto thee, arise, and take up thy couch, and go unto thine house.” The ye refers to the scribes and Pharisees who were present; it is a plural form. Then there is a switch to thee, thy, and thine as the afflicted man alone is addressed in the familiar form.

One more observation: just as the article a is used today in front of a consonant sound and an is used in front of a vowel sound, thy was used in front of a consonant sound (thy leg trembles) and thine was used in front of a vowel sound (thine arm trembles).

I'm telling thee, tymes were different.