Zeal in the Bible means something fairly specific. It essentially is a byword for an uncompromising devotion to the sole sovereignty of God. That concept—the sole sovereignty of God—is in many ways the very foundation of the Hebrew Scriptures. It is the first and most important commandment. It is of course part of the very DNA of the Israelites and the nation of Israel, that there is just one king, not just over this land but over all the universe, and that you are to, not just worship no other god, but to have no other master, which is why all the great heroes and prophets and kings of the Hebrew Scriptures were all praised for their zealousness, for being zealous for the Lord.
This concept of zeal and zealotry was very much present in the first century, in the time of Jesus and was, as the great Jewish historian Josephus refers to it, a kind of virus that spread through the land, and it’s no surprise. I mean, after all, the Jews in Jesus’ time were living under a brutal military occupation by a heathen, pagan power that lived a thousand kilometers away that controlled almost every aspect of life for the Jews from the economy to politics, to even the religious cult itself.
It shouldn’t be surprising, therefore, that for poor, pious Jews in particular, the revival of this concept, of biblical zeal, provided an impetus for standing up against the occupation, for pushing back against it, for calling for the liberation of the Jews and the cleansing of this land as God had intended in the first place.