Blessed are the pure of heart. For they shall see God.
Mary had the purest of hearts. She may very well have seen and understood what God was up to by allowing his only son (and hers) to be condemned to die by crucifixion. She may well have perceived the beauty of God’s sacrificial love and it would have been experienced as a sort of piercing cupid’s arrow, overwhelming her with the inexpressible depth and passion of God toward humanity. And it’s possible she alone could see this plainly and instantaneously, even before the final outcome of the resurrection.
It’s possible she didn’t understand and simply stood at the foot of the cross grieving in total trust, but it’s also possible her pure heart may have allowed her to understand that this was none other than God’s emphatic expression of his boundless love for us. There’s little doubt that this would have been a deep form of suffering either way.
In fact, there would be an interesting and novel thing taking place here. God, in the form of the man Jesus, would be suffering in a way most foreign to divinity, while Mary his mother, a mere human being, would be suffering in a way most foreign to humanity up to that point in history.