Adam Clarke on Matthew 27:51

The veil of the temple was rent - That is, the veil which separated the holy place, where the priests ministered, from the holy of holies, into which the high priest only entered, and that once a year, to make a general expiation for the sins of the people. This rending of the veil was emblematical, and pointed out that the separation between Jews and Gentiles was now abolished, and that the privilege of the high priest was now communicated to all mankind: All might henceforth have access to the throne of grace, through the one great atonement and mediator, the Lord Jesus. See this beautifully illustrated in Heb 10:19-22.