The Cross in Sons of the Forest serves a specific purpose when facing certain enemies. According to available information, its primary use is focused on combating Demons.
The main purpose of the Cross is to fight Demons. While you won't encounter these particular enemies until later stages of the game, obtaining the Cross early is straightforward and recommended.
To utilize the Cross effectively against Demons, the method is direct: you simply aim at Demons to set them on fire. This action triggers the Cross's effect, neutralizing the threat posed by these creatures.