The following article by Thomas Farrar, a former Christadelphian, discusses δια plus the genitive and the creative role of the Lord Jesus Christ in the theology of the Greek New Testament, refuting the view of Socinians (e.g., Christadelphians; Anthony Buzzard; Charles Hunting; Dustin Smith) that Jesus only had a notional, not personal, pre-existence:
He also has a good article on his blog on a similar issue, On prepositions and pre-existence, wherein he summarises the work of Gregory E. Sterling's article, Prepositional Metaphysics in Jewish Wisdom Speculation and Early Christian Liturgical Texts that appeared in The Studia Philonica annual, volume 9, pp. 219-238 (I own this volume and highly recommend this fascinating series of essays, especially Sterling’s).