The search for the "Philosopher's Stone" was the central feature of European alchemy. The Stone was believed to be capable of transforming base metals into gold and to have other transformative, healing and perfecting powers. (Alchemy also has a long history in China, but there the search was focused mainly on ways to prolong life.)
It is simplistic to view alchemy as nothing more than the search for a way to make gold from lead. It is also demonstrates a very narrow view of the history of the development of philosophy, religion and science to state that those who engaged in alchemy were nothing more than credulous, greedy fools. It is true that there were alchemists who focused exclusively on the manipulation of materials in a purely physical way in their search for some way to convert lead to gold, but they were dismissed as mere "puffers" (a reference to the bellows used to stoke fires) by those who viewed alchemy as being a highly spiritual and deeply philosophical practise as much as a complex physical activity.
Many of the best minds of their time engaged in alchemy and most of them were also devout Christians. For many alchemists, prayer and religious activity were as important in their work as the manipulation of physical materials by various means.
Today, gold is seen as an element whose particular properties are due to its peculiar arrangement of elemental particles. To an alchemist, gold was a perfect metal and therefore nearer the Divine than other minerals. In the universe of an alchemist, the Philosopher's Stone would remove the base, earthly impurities in, for example, lead and thus permit it to become the "perfect" metal.
One of the underlying beliefs of alchemy is that since God is perfect, therefore anyone who helps the universe in some small way to be more perfect is doing God's work.
Many alchemists also believed that the exterior work seeking the Stone and it's transformation of base metal in to noble metal would be mirrored internally in a spiritual sense and they would themselves become more spiritually perfect as the result of "The Great Work".
While European alchemists clearly considered themselves Christians - and some were almost fanatically devout - the idea that their efforts would improve the state of their soul is clearly at odds with the present interpretation of the bible by some varieties of modern Christian who believe that it is not possible to be saved by our works, but only by believing in Jesus. While I have read of alchemists being jailed and executed by civil authorities on grounds of fraud or theft, I don't recall ever hearing of alchemists being punished or excommunicated by the Church on the grounds that what they were doing was in conflict with Christian teachings. However, I'm neither a theologian nor an historian, so it is entirely possible that such persecution did indeed take place.