No problem! It certainly doesn't make sense if one approaches it from a Western Christian mindset. I am not trying to imply that is how you are approaching it, rather I mention this because Judaism often gets compared to Christianity, but I think they are quite different.

It is better to think of Judaism as a tribe. Membership to this tribe is mainly given under two conditions: through matrilineal descent or through religious conversion. Some subgroups within the tribe have different membership conditions like recognizing patrilineal descent, others may not recognize conversions done by other subgroups.