de que se trataba

[BBGirl]

Even though I've read all of the entries on "se trataba" I can't understand this sentence below (part in blue)

Could someone enlighten me?

En este segundo encuentro muchas cosas le preguntó y para estar seguro de que se trataba de la Madre de Dios, le pidió una señal.

 

[isabel.eim]

... and to be sure she really was God's Mother

 

[Frank Furt]

The verb "tratarse de" (here) means "really be":

(...) and in order to be sure she really was God's Mother, he(she?) asked for a signal.

 

[flljob]

En este caso quiere decir para estar seguro de que era la madre de Dios...