Latin Sigillum was the diminutive
of signum, and thus a little sign or symbol. Parsed through Old
French and Middle English, the word became seel, which by the 13th
century was a device with a raised or incised emblem that could be impressed
on wax to certify a signature or authenticate a document. Very early, "seal"
gained the implication of formalizing a transaction, so that early religion
spoke of souls "sealed" to God. A wax or lead seal might even be used to
close up a folded or rolled document or letter so that the recipient could
be sure it had been safe from prying eyes, giving rise to the sense of
physically closing or securing a letter or package. Seals were also common
in commerce and shipping to demonstrate that jars, bales, bags and boxes
were whole and uncontaminated.
"Deliver" first meant to set free,
a sense retained in a jail delivery (jail break) and in "deliver us from
evil." The Latin root is liber, "free" as in liberty, liberal, supposedly
derived from an IE root meaning grow, mount up. AHD confides that "the
precise semantic development is obscure." The best guess I've seen is that
liber originally meant a nobleman (i.e., someone who has been raised
up) and came to mean free by association. (The similar appearing words
deliberate, libra, liter, etc., are from a non-Indo-European root lithra,
meaning weigh or scales.)
In its legal usage, "signed, sealed and delivered" has (or had, at least) a very narrow and specific significance. "Signed" is equivalent to "given by hand" or "given under my hand" and requires that the maker of a deed, grant or promise personally execute it, by mark or signature. "Sealed," now obsolete, meant that the maker had, in addition, affixed his seal, which was significant not to prove who the maker was (as a modern lawyer might think) but to waive any objection that the document (whatever it was) was not supported by adequate value received. A modern lawyer would understand "sealed" to mean that a notary has attested or authenticated the signature on the document. "Delivered" was particularly important for deeds and gifts-a gift or grant does not take effect until the property or a deed to the property is placed in the hands of the grantee or donee. In medieval practice, "livery of seisin" (literally, delivery of possession) required that if I wanted to grant you a piece of land, I had to go upon the property with you and hand you a clod of dirt from the land. For urban land, I would hand you the key to the front door.