At the time of Jesus, many Jews worked hard to spread their unique religion of one God around the world. At the same time, there were some people who were fed up with the Greek myths and their quarreling gods. They took pleasure in knowing that the Lord is One, and were delighted with the Ten Commandments and in God's well-arranged law. But these initial conversions shown by circumcision and dipping into water eventually decreased. The focus was placed instead on disputes on legislative and jurist principles, and on what was acceptable and what was unacceptable. The orthodox turned to the observances and became more hardened than the hypocritical Pharisees. This spirit of legalism lead to hardening, and not salvation. This is why Jesus had to speak of the opened mouth of hell to the hypocrites and scribes.
Various faiths accepted the concept of a single God with the obligation of His law, establishing their civilizations on piety and the fear of God. They threatened people with severe and dreadful punishments so that they might not transgress the law. Yet, they did not comprehend God's meek Lamb. They refused reconciliation with God, and changed the meanings of His Word. They did not learn of renewal based upon the cross, did not seek to love their enemies, and had no spiritual peace in their hearts. Furthermore, they opposed the unity of the Holy Trinity. Christ died for them and sought to reconcile them to God, but they rejected (and are still rejecting) the salvation offered to them.
It is sad to think how many are under the guidance of such blind leaders, who try to show others the way which they are themselves ignorant of. "His watchmen are blind" (Isaiah 56:10). Often, the people love it that way, and prefer that the seers see not! But it is bad when the leaders of the people "cause them to err" (Isaiah 9:16). Though the condition of those whose guides are blind is sad, that of the blind guides themselves is worse. Christ announces woe to the blind guides that have the blood of so many souls to answer for.