I've read Rahner. I still think he's a Modernist of the worst sort. His Eucharistic theology and his ecclesiology were both heretical. And as for "bringing Catholic theology into the modern world" you mean deforming Church teaching and leading to the "hermeneutic of rupture" that Holy Church is only just beginning to escape?
The basis of Karl Rahner's theology is that God has endowed man with a transcendental experience of an "infinite horizon" which is in the background of all our experience. It is a "holy mystery" because it wants to fulfill our spiritual destiny and cannot be contained by any category. The foundation of the capacity for this experience is what Rahner calls God's self-communication to man--i.e. grace.
God's self-communication to man demonstrates that God wants to give himself to us and to "draw near." The high point of God's gift of himself to man is the life, death, and resurrection of Jesus Christ. Most of Karl Rahner's theology relates in some way to what I just described.
Karl Rahner's first philosophical works were "Spirit in the World" and "Hearer of the Word." His most systematic work is "Foundations of Christian Faith." Rahner's most comprehensive and wide-ranging work is the 23-volume "Theological Investigations." He also wrote spiritual works such as "Encounters With Silence."
When I said that Karl Rahner brought Catholic theology into the modern world, it is because he felt it necessary to apply Thomism to the developments in knowledge since the Middle Ages. He engaged with the knowledge base of the modern world in areas like biblical scholarship, history, anthropology, philosophy, and evolutionary theory. It is in this manner, he felt, that Christianity and Catholicism can give an intellectually credible witness in the modern age.
(see Steven Buller: "The Theology of Karl Rahner: A Restatement of Foundations of Christian Faith."
Also, Karen Kilby, Leo J. O'Donovan, M. Edmund Hussey, etc.)