ירמיהו יב:יג פירוש: רש״י

They sowed wheat, but they reaped thorns They prayed, but their prayer was not accepted. Why? Because they did not plow for themselves a furrow of repentance and good deeds. Therefore, they sowed seeds resulting in thorns. A book in which זרעו is vowelized with a ‘chirik’ under the ‘zayin,’ is erroneous.

they have become ill Heb. נחלו, an expression of illness. They have become ill with their pain and their cry before Me, but they did not avail.

of your increase Of your deeds.