What, according to Philo Judaeus, is attractive about Judaism, and especially its ethics? In order to answer this question I will in the introductory section of the paper look more generally at the dynamics of attraction to Judaism by Greeks and Romans in antiquity. We will then turn to the question what Philo thought to be distinctive and attractive about the Jewish faith. We will look at Philo’s universalism and the role that Israel and the law have in this aspect of his soteriology. The central virtue of piety as the foundation of ethics will be discussed. Unlike the thinkers in the Hellenistic philosophical traditions who subordinated piety to righteousness or to another virtue, Philo believes that it serves as the source for all other virtues. A major argument of the paper is that for Philo piety is also the source of ethical enabling. It is in an intimate relationship to the One Who Is that people get transformed and empowered for ethical living. I will show how Philo differs in this regard from Stoicism, although also for Philo pneuma plays an important role in his theology. In Philo the Spirit enables this intimate, empowering relationship to God (e.g. Leg. 1.38–39; QuaestExod. 2.29; Gig. 54–55). The Spirit thus is a facilitator of ethical life. In the concluding section we will glance at the Wirkungsgeschichte of Philo’s ethics. Although there appears to be little explicit interaction with Philo in the immediate aftermath of his writing, I will demonstrate at the example of 2 Corinthians 3:18 how the Philonic tradition of ethical transformation as the consequence of mystical encounters with the divine, as well as the facilitating role that is played by Spirit in this process, has had an impact on key figures in the formation of the New Testament.