This is the most thorough resource I’m aware of that explains why the temple’s curtain tore in two when Jesus died:
Daniel M. Gurtner. The Torn Veil: Matthew’s Exposition of the Death of Jesus. Society for New Testament Studies Monograph Series 139. Cambridge: Cambridge University Press, 2007.
It focuses on Matt 27:51a but takes into account the other Synoptic references and the explanations in Hebrews.
Dan Gurtner teaches New Testament at Bethel Seminary in St. Paul, Minnesota and serves as an elder at Bethlehem Baptist Church (where John Piper is pastor for preaching and vision). He earned his PhD at the University of St. Andrews in Scotland under Richard Bauckham, and this book is the published version of his dissertation on the tearing of the temple’s curtain in Matthew 27:51a.
Among other things, Gurtner convincingly argues that the temple curtain that tore is the inner veil that separated the Holy Place from the Most Holy Place (the Holy of Holies).
Cf. D. A. Carson, “Matthew,” in Matthew–Mark 
(Revised Expositor’s Bible Commentary 9; Grand Rapids: Zondervan, 2010), 649–50:
If the death of Jesus opened up a fresh access to God that made the OT sacrificial system and the Levitical high priesthood obsolete, then an entire change in the Mosaic covenant must follow. It is impossible to grapple with Matthew’s fulfillment themes (see comments at 5:17–20; 11:11–13) and see how even the law points prophetically to Messiah and hear Jesus’ promise of a new covenant grounded in his death (26:26–29) without seeing that the tearing of the veil signifies the obsolescence of the temple ritual and the law governing it. Jesus himself is the New Temple, the meeting place of God and man (see comments at 26:61); the old is obsolete. The rent veil does indeed serve as a sign of the temple’s impending destruction—a destruction conceived not as a brute fact but as a theological necessity. For extensive discussion, see Daniel M. Gurtner, The Torn Veil: Matthew’s Exposition of the Death of Jesus (SNTSMS 139; Cambridge: Cambridge Univ. Press, 2007).
Related: Justin Taylor, “What Did the Temple Look Like in Jesus’ Time?”
Andy, thanks for the recommendation here. When is the audio from your message going to be up?
I preached on the tearing of the veil at my church’s Good Friday service last week, but I don’t think the audio would be terribly helpful even if it were available because the presentation was so visual: I had 27 slides, mostly illustrations of the tabernacle and the Jewish temples.
:(
If there’s a demand, I’d be willing to splice them together into a Vimeo if you’d send me the stuff! :)
Andy & Matthew, I would appreciate seeing the presentation. Also, this book looks like a wonderful resource. Thank you for recommending it.
Andy,
It wouldn’t take me very long, I’m sure. And almost zero time for you. All I’d need is your presentation file (PowerPoint?) and the audio file. I could figure out the transitions myself. Then I’d send you a proof copy before final publishing.