I encourage you to read the whole letter but here is one quotation:
I believe that this moment has brought to the fore as no other in recent times a critical question: that of the understanding and interpretation of the Second Vatican Council. Was it to be seen as a rupture with all that went before, so that nothing in the Church’s life and teaching was to be exempt from change, indeed a process of continual mutation to fit in with the perceived demands and approvals of contemporary thinking and behaviour? Or is the Council and the subsequent life of the Church to be understood in unbroken continuity with the Church of all ages, passing also through our particular ‘modern’ stage of her long journey through time towards her Lord, united as ever in one faith, one hope and one love, always one in her doctrine, her worship and her sacramental life? It is this question which the Holy Father, with all the affirmation of faith, seems to me to be helping us to understand.