There arises at some point the at least theoretical threat that if one gives a Protector the power to both fire and appoint a Trustee, the Protector will appoint herself as the Trustee.

FORBES: Trust Protectors -- What They Are And Why Probably Every Trust Should Have One

These words already point to the mission which God entrusts to Joseph: he is to be the custos, the protector.

CNN: Text of Pope Francis' homily