The tragedy of martyrdom was entirely the Divine mercy. It constituted a proof of (Divine) love and Yazid was void of it. The fact is that the Imams, the Prophet and the parents of the Imams had got reconciled with the Divine will for the later scheduled martyrdom of the lmam,as the Prophet’s followers were to benefit from it.

Marty's tribulations are in fact God's mercy rain,
Yazid is quite unware of such divine grace,
To sacrifice themselves was fathom Karbala's tragedy's depth.

The hardship of martyrdom was a rain of mercy,
Yazeed knew not, it was a sign of love,
The Imams have an eternal covenant to die.