In 2 Cor. 12:2, Paul refers to a third heaven. What does he mean by this and what does the church teach on the number of heavens?
The Catechism defines heaven as a state of being: “Eternal life with God; communion of life and love with the Trinity and all the blessed. Heaven is the state of supreme and definitive happiness, the goal of the deepest longings of humanity” (CCC Glossary). As such, there is only one heaven. In his second epistle to the Corinthians, Paul seems to be distinguishing between that heaven and levels of the sky/space.
*A Catholic Commentary on Holy Scripture * explains, “he is using the language of some astronomical system which he had heard of (there were many). He certainly means the highest (or farthest) sphere, regarded as the place where God dwells”.
The Navarre Bible also states, “according to some commentators, this simply refers to the situation in which the blessed dwell, that is, the most sublime level of divine contemplation. Others see in it an echo of Jewish traditions which spoke of a first heaven (the atmosphere of the earth), a second (the heaven of the stars) and a third (the dwelling-place of God). In any event, “Paradise” (v. 4) would have the same meaning”.
For additional information see Whether There is Only One Heaven?