עזרא, פרק ט׳, פסוק ב׳

The blurring of boundaries between the Israelites and the surrounding nations sparked a severe spiritual crisis. A growing sense of closeness to their neighbors led directly to intermarriage, which became the root cause of the people adopting foreign practices and abominations [מצודת דוד, מלבי״ם, ביאור שטיינזלץ].

The Israelites, identified as the holy seed [מצודת דוד], mixed with the local populations by taking foreign women as wives for themselves and their sons. This mingling reveals that the marriages took place while the women retained their foreign status, without undergoing any conversion. Had they converted, there would have been no restriction against marrying women from these surrounding nations [רלב״ג].

The gravity of this betrayal is magnified by the source of the problem. Typically, assimilation begins among the common people at the margins of society. In this case, however, the dynamic was completely reversed. The high officials and leaders of the nation were the very first to intermarry, likely driven by a desire to align themselves with women of high social standing [רש״י, מלבי״ם, ביאור שטיינזלץ]. Their actions were deeply destructive because they set a poor standard that the rest of the nation simply observed and copied [מצודת דוד, ביאור שטיינזלץ]. Throughout all of this, it appears that Ezra remained entirely unaware of the unfolding crisis until the moment it was finally brought to his attention [ביאור שטיינזלץ].