Susan's answer is a good example. I will also show you the same answer, however, in a more simple form:
A (VERY) BRIEF HISTORY OF THE ENGLISH LANGUAGE
The Lord’s Prayer
It is interesting to compare various versions of a Christian prayer (The Lord’s Prayer) as a good example to see the differences between Old, Middle, and Modern English.
Old English (500 – 1000 AD)
Fæder ure þuþe eart on heofonum
si þin nama gehalgod tobecume þin rice gewurþe þin willa on eorðan swa swa on heofonum
urne gedæghwamlican hlaf syle us to dæg
and forgyf us ure gyltas swa swa we forgyfað urum gyltendum
and ne gelæd þu us on costnunge ac alys us of yfele soþlice.
Middle English (1000 – 1500 AD)
Some of the words are recognizable to the modern eye:
Oure fadir þat art in heuenes halwid be þi name;
þi reume or kyngdom come to be. Be þi wille don in herþe as it is dounin heuene.
yeue to us today oure eche dayes bred.
And foryeue to us oure dettis þat is oure synnys as we foryeuen to oure dettouris þat is to men þat han synned in us.
And lede us not into temptacion but delyuere us from euyl.
Early-Modern English (1500 – 1800 AD)
Late-Modern English (1800 – present)
The words are completely intelligible:
Our father which art in heaven, hallowed be thy name.
Thy kingdom come. Thy will be done in earth as it is in heaven.
Give us this day our daily bread.
And forgive us our debts as we forgive our debters.
And lead us not into temptation, but deliver us from evil. Amen.