At Jesus' death Luke reports that the veil of the Temple was torn in two. Modern readers may picture a decorative curtain, but curtains in the Jerusalem sanctuary were associated with access, separation, and sacred space.
The event therefore carries meaning precisely because of where such a veil belonged.
The Temple contained curtains associated with its sacred zones, including the veil connected with the innermost sanctuary. Ancient descriptions also mention a curtain at the sanctuary entrance. The Gospel writers do not provide enough architectural detail to settle every question about precisely which curtain they intend.
In either case, a torn sanctuary veil is a dramatic disruption of a boundary within Israel's central place of worship.
The Temple background keeps the sign from becoming merely a supernatural special effect. Something associated with sacred separation is torn at the moment of Jesus' death.
Christian interpretation has naturally connected this with access to God through Christ, especially in light of Hebrews. Luke himself presents the tearing as one of the signs surrounding the crucifixion and leaves its symbolic force to resonate within the larger biblical story.