The Lord spoke harshly to Judah through the prophets, because they needed to hear it and they needed to hear it in the fashion that the prophets delivered the Lord’s message.
However, He also spoke kindly and with promises of great things, such as when He announced after national repentance, that they would return to Him, and He said,
“Those of Ephraim shall be like a mighty man…they shall increase as they once increased. I will sow them among the peoples, and they shall remember Me in far countries…” (Zechariah 10:7–11).
The Lord wants to bless, but He often has to rebuke, even severely, before He can bless so that people might turn to righteousness first.