This is a beautiful invitation from a profound thinker and father. I see in it a great theological space for reflection on the Jesuit's fourth vow in the contemporary theological context. Any thoughts on how that should look? Here's a quote from Benedict's recent audience with GC35:
For this reason I have asked a renewed effort on your part to promote and defend Catholic doctrine, "in particular those neuralgic points of doctrine under heavy attack today from secular culture," some examples of which I gave in my Letter. The issues of the salvation of all men in Christ, of sexual morality, of marriage and family -- issues constantly debated and called into question today -- will become more deeply and clearly understood in the context of contemporary reality, if one maintains that harmony with the Magisterium which avoids causing confusion and distress among the People of God.
I well understand that this is a particularly delicate and troublesome issue for you and for many of your companions, especially those engaged in theological research, in inter-religious dialogue, and in dialogue with contemporary cultures. Precisely for this reason I have invited you in the past and I invite you again today to consider how to regain a fuller meaning of your distinctive "fourth vow" of obedience to the Successor of Peter -- which consists not solely in readiness to be sent on mission to distant lands, but also -- in the more authentically Ignatian spirit of "thinking with the Church and in the Church" -- in the the readiness to "love and serve" the Vicar of Christ on earth with that "effective and affective" devotion which must make you his precious and irreplaceable co-workers in his service for the universal Church.