The works of Philo is a great resource for understanding one perspective on Jewish culture, history, and theology at the time of Jesus. Alongside other sources like Josephus, the Mishnah, the Talmud, and the Dead Sea Scrolls, Philo gives us another glimpse into what first century Judaism was like, which is very helpful in understanding the New Testament.
In this age of extreme historical scepticism it is good to have the writings of an opponent of Christianity whose writings in some way corroborate the truth-claims of the early Christians, as the writings of Philo do. I find it both fascinating and edifying. As a Christian pastor it helps me to put across the faith better, both to modern sceptics and to modern Christians. It is a witness from the ancient world that we ought not to ignore.