Text: Mt. 23:15 (NET) "Woe to you, experts in the law and you Pharisees, hypocrites! You cross land and sea to make one convert, and when you get one, you make him twice as much a child of hell as yourselves!
Matthew 23:15 alludes to Jewish converts of Rome who were raised pagan diefying Caesar and later became children (students) of Pharisaic Judaism.
Pharisaic Judaism believed in the Torah but also traditional man-made laws which regarded both the "lack of washing hands before eating" or "tearing grain on the Sabbath" as sins requiring atonement.
Pharisaic laws misinterpreted the Torah. - Yeshua (Jesus) of Nazareth teaches this correction to help Pharisees interpret Deuteronomy 23:26 literally in Mark 2:23-24.
[Devarim 23:26] "When you enter your neighbor's standing grain, you may pick the ears with your hand - but you shall not lift a sickle upon your neighbor's standing grain." ( כִּ֤י תָבֹא֙ בְּקָמַ֣ת רֵעֶ֔ךָ וְקָֽטַפְתָּ֥ מְלִילֹ֖ת בְּיָדֶ֑ךָ וְחֶרְמֵשׁ֙ לֹ֣א תָנִ֔יף עַ֖ל קָמַ֥ת רֵעֶֽךָ)
Many don't realize that the Pharisees were an extermely evangelical sect in Jesus day, and sent out many missionaries all over Rome. They had special dispensation from Rome to proselytize outside their native province, something not given to other religions (and something Christian missionaries piggy-backed off of, considering themselves jews, to the consternation of the Pharisees who would then report them to local authorities). Several of the famous rabbis that wrote the Talmud were the children or grandchildren of converts.
But the converts of the pharisees were twice the child of hell because now they were under two laws, the laws of their pagan society and the laws of the pharisees. This is also a parallel to being born again, except you are born twice into sin, and thus twice the son of hell.