In order to really get a good understanding of Christian theology and Christian philosophy, you first need a solid foundation of understanding Plato’s philosophy.
There’s just no way around it. Even Paul’s writings contain Platonic thought and ideas.
Plato’s philosophy still heavily influences Christianity today as well – for instance, our ideas about body/soul dualism, the afterlife, the spiritual being greater than the flesh/material, repentance, conversion, etc.
Here are some summaries we wrote about Plato’s and Greek philosophy’s impact on Christian thought here in terms of church history.
Here is Prof. Andrew Davison of St. Johns College, Nottingham, UK, talking about how Plato influenced Christian philosophy – especially that of Augustine, who was heavily influenced by Plotinus and Neoplatonism.