This was where Jean-Baptiste spent most of his childhood. However, little is known about him during that period besides his charitable deeds and his education at the Jesuit College in Grenoble. The La Croix children were much influenced by religion; three out of ten entered religious life. Jean-Baptiste entered the seminary of Saint-Sulpice in Paris and obtained his licentiate in theology in 1672 at 19 years of age. In 1676, he was appointed almoner-in-ordinary to King Louis XIV, a promotion that can be attributed to his family's connections. He was ordained priest in 1681. He personally funded a small hospital in Saint-Vallier in 1683.