The rending of the temple veil, Matt 27:51, probably had two significances:
1. It was a supernatural act
The dividing veil between the Holy Place and Most Holy Place was a very heavy material that was both strong and very high (18 m according to the OP's source). No man or even a group of men could have torn it.
Further, the record states that the curtain was ripped from top to bottom eliminating any possible human source of the tear!
The only possible way such an unnatural act could have been achieved is by supernatural means, perhaps by an angel or by order of God.
2. Type Met Antitype
The rending of the temple veil clearly signified that all the symbols in the sanctuary ritual such as sacrificial lamb, the true significance of Passover, etc, etc, had met their fulfilment in Christ Jesus. That is, the entire ceremonial system was a teaching system to inculcate the plan of salvation, Heb 9:8, 9, 11-14, 10:1, Col 2:16, 17.
There could be no clearer sign that that this was indeed a divine act signifying that the ceremonial system had ended.
Henceforth, sinners had direct access to the heavenly Father-God via the High Priest of Jesus Christ, Heb 4:14, 15, 7:26-28, etc.
This opens a third possible significance for the rent veil:
3. The way into the heavenly Holy of Holies was now open
Heb 6:19, 20 - We have this hope as an anchor for the soul, firm and
secure. It enters the inner sanctuary behind the curtain, where
Jesus our forerunner has entered on our behalf. He has become a high
priest forever in the order of Melchizedek.
Heb 9:24, 25 - For Christ did not enter a man-made copy of the true
sanctuary, but He entered heaven itself, now to appear on our behalf
in the presence of God. Nor did He enter heaven to offer Himself again
and again, as the high priest enters the Most Holy Place every year
with blood that is not his own.