The Bible is loaded with allusions to other books of the Bible, without explicitly saying so, presuming the reader is already familiar with it. Less commonly, the Bible also makes allusions to (sometimes explicit references, other times allusions) 3rd party non-Biblical works - sometimes fiction (that everyone knew was fiction), sometimes history records (i.e. annals of the kings, or annals of religious groups), sometimes artistic works, sometimes philosophical works, sometimes Hebrew, sometimes Gentile, sometimes pagan.
I'm interested in how this practice developed...
So where did allusion begin, across novels, plays and poetry, and
what was the literary purpose of the earliest example?
There are several literary purposes of the Bible's allusions. One is to establish theological concepts, that later can be referred to and built further upon. Basically serving the theological equivalent of a Design Pattern (computer programming), Trope (entertainment), and technical inspeak (e.g. in engineering). Complex ideas can be easier to comprehend if you break them into bite-size self-contained chunks that can be referred to with a single word or sentence. Like lego blocks, you use multiple self-contained concepts to build a larger structure.
Another Biblical purpose of allusion is to reference history, to then explain something philosophical or theological on top of it. If I want to draw a theological lesson out of WW2, I don't need to re-explain what WW2 was, I can just say, "When Hitler invaded France...". Since the Bible contains a lot of Israel's history, authors in later parts of the Bible can make reference to earlier parts of the Bible using a mere phrase from that earlier part, to reference and then build upon a whole chunk of history.
Sometimes the Bible just mentions the history itself, "...the two tablets of stone which Moses put there at Horeb, where the Lord made a covenant with the sons of Israel...",
sometimes it references the work explicitly, "In the Laws of Moses..."/"The commandments of the Lord",
sometimes it just makes allusions, "you are a letter of Christ, delivered by us, written not with ink but with the Spirit of the living God, not on tablets of stone but on tablets of human hearts.". (tablets of stone here is a reference to the ten commandments, but whereas God's finger carved the ten commandments in stone tablets, God is (symbolically) writing his Words on their hearts).
Another literary purpose of allusion in the Bible is to reference other concepts that are disagreed with, and then provide a theological rebuttal to them, or to reference a non-Biblical idea someone already agrees with, a then use it as a jumping off point to direct them toward God.
Then Paul stood in the midst of the Areopagus and said, “Men of
Athens, I perceive that in all things you are very religious; for
as I was passing through and considering the objects of your worship,
I even found an altar with this inscription:
TO THE UNKNOWN GOD.
Therefore, the One whom you worship without knowing, Him I proclaim to
you:
Therefore, the One whom you worship without knowing, Him I proclaim to
you: God, who made the world and everything in it, since He is Lord
of heaven and earth, does not dwell in temples made with hands. [Allusion to Seneca the Younger] Nor
is He worshiped with men’s hands, as though He needed anything, since
He gives to all life, breath, and all things. [Another Seneca allusion] And He has made from
one blood every nation of men to dwell on all the face of the
earth, and has determined their preappointed times and the boundaries
of their dwellings, so that they should seek the Lord, in the hope
that they might grope for Him and find Him, though He is not far from
each one of us; for in Him we live and move and have our being, as
also some of your own poets have said, ‘For we are also His
offspring.’ [Aratus] Therefore, since we are the offspring of God, we ought
not to think that the Divine Nature is like gold or silver or stone,
something shaped by art and man’s devising. [Seneca] Truly, these times of
ignorance God overlooked, but now commands all men everywhere to
repent, because He has appointed a day on which He will judge the
world in righteousness by the Man whom He has ordained. He has given
assurance of this to all by raising Him from the dead.”
And when they heard of the resurrection of the dead, some mocked,
while others said, “We will hear you again on this matter.”
Paul quotes Plato and Plato-Socrates several times in other letters, who lived 450 years before Paul. But as you can see in the above passage, he also alludes to Seneca the Younger quite a few times, who was a prominent Greek philosopher who was alive and popular at the same time Paul was engaging in ministry.
Paul, in his arguments, very very often references Greek philosophy, since he was classically taught as a Roman citizen, and his ministry was mostly to Greek areas of the world. He was not stealing from Plato to speak to rural non-Greeks unfamiliar with Plato's works, but was quoting Plato and Seneca to speak to highly educated Greeks in large wealthy Greek cities who would instantly recognize the allusions.