By Luke Lancaster
To understand the development of doctrine, consider three analogies:
You write out a general outline with three main points in a paper on day one. Then, during your investigation, you narrow down the specifics of point number one for one week. Next, you research point number two during the next week, and point number three during the final week. This is similar to how the Church received a large body of teachings about general realities, such as Mary, Church leadership, or life after death. Then, over the last 2000 years, those ideas were debated and clarified, such as bishops governing set dioceses made up of priests and deacons.
You get married to the man or woman of your dreams, and then realize while living with them over time the various specific details about them that weren't very clear from the get-go. Maybe your spouse seemed to be a little distracted at times when you were dating, but when you got married, you realized that this was probably due to attention-deficit disorder. Similarly, the Church knew that man was "dead" before being saved by Jesus, but over time, She realized that this was due to the Original Sin of Adam and Eve losing their sanctifying grace.
Imagine you went to literature class to learn about C.S. Lewis's series, "Narnia," and wrote down a ton of notes. While reflecting on your notes and talking about them over dinner, you make a few connections and raise a few questions you hadn't thought of before. Similarly, Catholicism has had many "aha" moments throughout Church history. For example, if Mary is called the title "full of grace" by the Archangel Gabriel in Luke 1:28, then that would seem to indicate that Mary is totally filled with God's life. Now, we are totally filled with God's life only when we get baptized, yet, Mary's "status" seems to be a consistent "full cup" of grace. When would this have happened? Her first moment of existence: conception (i.e. the Immaculate Conception).