The Occasional Observer

Doesn’t the Catholic church teach that the Pope is infallible?

No, it doesn’t. It teaches that under certain circumstances, the Pope can teach infallibly. In practice, the Pope has only claimed to be teaching infallibly 2 times since Vatican I (1870? IIRC). You should explore what the Church claims, becuase it makes a compelling case for itself. This is especially true if you hold the Bible as the sole source of authoritative teaching about God, since it is through the Church that the Bible was received, understood, and carried forth to the world.

How, then, is it possible that rulings that come from the Vatican change over time?

When teaching on matters of faith and doctrine, where Catholic Christians believe the Church (not the Pope) is infallible, there have not been changes in doctrine of the type you seem to feel there has. There has been growth in teachings, where later teachings expand upon earlier teachings, but never contradiction. Examples would be teaching on the nature of the Eucharist, which was rooted as early as the first apostles and their followers, but which were not formalized and expanded upon until much later (St. Thomas Aquinas). Using our rational capacity to gain a greater understanding of the mystical truths that God has revealed to us is, it would seem to me, a good thing. Applying these received truths in an ever changing and modernizing world requires both a teaching authority and the use of our rational capacity to expand upon earlier teachings in a way that is consistent with earlier teachings.

BTW, originalists would be proud of this growth, as it is grounded in earlier texts and not an attempt to throw previous texts under the bus in order to meet “fashionable thinking.” Oh, how pleased the liberals and MSM would be if the Church went the way of some other denominations in saying that contraception is morally neutral and abortion between a woman and her doctor (for example, “This church recognizes that there can be sound reasons for ending a pregnancy through induced abortion.”).