MIDRASH TEHILLIM
1.....(13.1)
How long, O LORD? ...
..."He called and they did not listen, so shall they call and I will not listen, said the Lord of Hosts." (Zechariah 7:13)
Rabbi Itzchak said, Measure for measure. The Lord declared, Four times did I ask - How long?
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"...How long will you refuse to observe My commandments and My teachings?" (Shemot - Exodus 16:28)
"...How long will this people reject Me? How much longer will they not believe in Me after all the signs I have performed in their midst?" (Bamidbar - Numbers 14:11)
"How much longer will this evil congregation..."(Bamidbar - Numbers 14:27)
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Four times will you also ask - How long? (Tehillim 13:2-3)
After I will have delivered you over to the four kingdoms [Babylon, Persia, Greece, Edom], you will cry out four times in your distress, How Long?.