Alien: Sun worshipers learned of the vrill worm by way of Jesus (John hurt) has come in contact with something alien. He seems fine even though they know he's not normal. The chest bursting scene is when they learn of the worms evil nature and how it kills the person/Their humanity and turns them into psychotic monster. It's actually the veill controlling them. Ripley is the Sun/Venus hero emphasized with her being triumphant over the beast with fire and her cat Jones.
The start of Catholicism to combat the worms plan of totally conquering humanity indefinitely. Also the ships name Nostromo is signficant. Picrel . Ripley is masculine so she's "our man"Part 2 comming up