The graves were opened

52 The tombs also were opened. And many bodies of the saints who had fallen asleep were raised, 53 and coming out of the tombs after his resurrection they went into the holy city and appeared to many (Mt 27:52-53).

Many otherwise conservative (or fairly conservative) scholars are skittish when they come to this incident. 

i) This incident is anomalous in the sense that this is the only place where it's recorded. However, in terms of biblical theology, it's not anomalous. 

This is a microcosm of the resurrection of the just. That's a fundamental hope and expectation in biblical eschatology. 

ii) I don't think it's coincidental that this takes place right after the death of Christ. This is God's way of showing that the death of the Redeemer made atonement for the sins of his people. Here's some graphic evidence. Ever since Adam and Eve were banished from access to the tree of life, death has been the fate of all mankind, including God's people. Here we have a token reversal, keyed to the vicarious atonement of Christ. 

iii) The incident in Mt 27:52-53 is a foretaste and pledge for what the future holds. 

iv) Although this passage has no direct parallel in other Gospels, the raising of Lazarus is roughly analogous (Jn 11).

v) If the Bible is to be trusted, then this incident is exactly what will happen on a massive, worldwide scale when Jesus returns. 

If you happen to be walking through a cemetery at the time Jesus returns, that's what you will see. Graves will open and the dead in Christ will rise. This is a picture we need to take seriously, for this is what the resurrection of the just entails. If Christian scholars balk at that, they have failed to take to heart and think through the implications of biblical eschatology in this respect. That's how it cashes out in concrete terms. It will be a very physical, dramatic, hair-raising event.

(Some premil positions view the effects of the Parousia as multistaged rather than simultaneous. But even if it's a delayed effect, that's still the effect when it happens.)

vi) Admittedly, the object of glorification ranges along on continuum. At one end are Christians alive at the time Jesus returns. They will be instantly transformed.

At the other end are Christians whose bodies have disintegrated. God will reconstitute the unique molecular pattern of their bodies, and reunite their souls to their bodies. But where the body is intact, this is what will happen.

vii) Some readers have been conditioned by horror flicks about the zombie apocalypse to superimpose a false image on the text. But this doesn't describe rotting corpses which lumber around. To the contrary, they will be restored to life, youth, and health. Healthier than they were in the mortal prime of life.

viii) Mt 27:52-53 raises more questions than it answers, but that's a mark of historicity. If this was fiction, it would be easy for Matthew to tie up the loose ends. Fiction is tidy, reality is messy. 

ix) Some critics think it's legendary because, if it really happened, it would be a famous event. However:

a) The only people in a position to recognize that these were former decedents would be contemporary friends and relatives living in Jerusalem. And that might come down to just a handful of witnesses.

b) Jerusalem suffered two devastating attacks by the Romans, resulting in massive casualties, massive dislocation of survivors, as well as massive destruction of written records.