I have no time to fairly and justly give you a recommended selection of his works - so if you are hoping for for an "introduction" to him I must diappoint you, at least for today. But then... perhaps (like some other great writers) almost any of his works are a suitable start. In this he is like the holograms of laser physics, a great analogy to certain even more mystical ideas: any fractional part of a hologram contains a representation of the whole image.
But actually, I was thinking about how one could easily have a "Jaki Advent Retreat" with his incomparable meditations on the Savior, and though there are barely two weeks left before Christmas, I suggest the following texts. (You can always work on obtaining them now, for future use.)
1. Advent and Science - a booklet of four essays
2. The Virgin Birth and the Birth of Science - a booklet with pictures by Blake
3. Catholic Essays - this is a collection but I mean specifically these two: "3. The Creator's Coming" and "4. A Most Holy Night"
You may also add, if you like, his little books on the Litany of Loreto and of St. Joseph, as well as the Magnificat...
I must also suggest his cosmological or Christocentric studies, though it would be to open not a retreat, but the bibliography for a grad-school seminar, and add items like his studies of the Psalms and The Savior of Science - but especially deserving of exploration is the important chapter on Science and the Jews, the seventh in Science and Creation which is called "The Beacon of the Covenant":
In the biblical view God is primarily and ultimately a person, whose most unique characteristic is to reveal His unspeakable transcendence in His most immediate concern for the children of Abraham.What a grand statement of What Advent Is All About...
The God of the Bible is the God of Abraham, Isaac, and Jacob; that is, the God of the Covenant, or a God who freely binds Himself to the welfare of mankind through the mediation of Abraham’s progeny.
[SLJ SC 139]
"...a God who freely binds Himself to the welfare of mankind through the mediation of Abraham’s progeny..."