First timer with a code..

This looks like a very interesting place. Last night while partaking
in some "herbal" therapy, I thought up a code. This is a code that can
be encrypted and decrypted using a key without any type of computer
program. In other words it can by done at both ends on a piece of
paper, or in your head if you are the really smart type.

I am attaching a sample to see if any of you find it blatantly obvious
how it works.

gefrlwfobdvwsrpkklemwatogavpefjiplmdelsqdligmvqpfbeqpkgzfomjpbmidomkmfcygolxmlitgoewtmelwmevpkaldelnplfiqpobrwhkdovhfeisdelmkjmirolhktumdeaqfeptfbengwzknoitktemfevreyctdoigavrufevstiwr

This is a simple plain English sentence.
.