द Da
娜字門一切法施不可得故
陀字門，諸法善心生故，亦施相故。
入柁字門，悟一切法調伏寂靜真如平等無分別故 (Xuanzang)
'Da' is a gateway because the generosity / giving (dana दान ) of all dharmas is unattainable.
the virtuous mind of all dharmas is generated by giving (dana दान).
(Sanskrit) - of the dānta-damatha-paricchinna (दान्त-दमथ-परिच्छिन्न) of all dharmas.
DA is a door to all dharms because "tamed" and "taming" (dantadamatha) have been circumscribed
Conze
The syllable DA is an opening because of the restraint, self-control, and circumspection (dānta-damatha-paricchinna) of all mental phenomena.
Jayarava