Why did early Christians adopt some of the images and symbols of their contemporary religions?

Answer 1

The early Christian leaders were anxious not only to convert the pagans, but to distract their allegiance from their former beliefs.

It was common practice that, where pagans were found to celebrate a particular feast day, the same feast day would be appropriated for a local saint. The people were expected to attend Christian festivities on that day, thus removing the chance of illicit pagan festivities.

An ancient Irish goddess, Brigid, was adopted by the Church as a Christian saint. Thus the folk memory of her would be explained away as a long-dead saint.

After Christianity became the state religion of Rome in 391, the Christian Church began to expropriate the pagan temples, which often still had valuable marble statues of their gods. Rather than destroy the statues of Jupiter, they were reassigned as statues of Saint Peter.

Answer 2

They feared persecution for their faith