"But you have planted wickedness, you have reaped evil, you have eaten the fruit of deception." NIV translation
Instead of the seed of repentance being planted in their hearts, the hearts of Israel contained the seed of self-reliance. Instead of producing gratitude and thanksgiving, their wealth and strength gave them a false sense of security. The fruit of deception is talking about the fact that they had the attitude that they did not need God. The same attitude is widespread in the world today and will be even worse in the last days.
"Because you have depended on your own strength and on your many warriors, the roar of battle will rise against your people, so that all your fortresses will be devastated - as Shalman devastated Beth Arbel on the day of battle, when mothers were dashed to the ground with their children." NIV translation
The fruit of this self-reliance is devastation.
Beth Arbel is located near the Sea of Galilee and the Shalman mentioned is probably a form of Shallum who became king of Israel. He assassinated Zechariah who was king at the time but Shallum only reigned for one month. (see 2 Kings 15)
This same deception will occur in the last days as Satan will get the leaders of the world to form an army to fight God. His rally cry will be that, if they all work together, they can win.
"So will it happen to you, Bethel, because your wickedness is great. When that day dawns, the king of Israel will be completely destroyed." NIV translation
Shallum was the fourth generation of Israelite kings through Jehu. Jehu was responsible for cleansing Israel from Ahab and Jezebel. God promised him that he would have four generations of kings in his line. His line was limited to four because he did not stamp out the idolatry that had been started by Jeroboam.
God uses this example from Israel's past to remind them of the consequences of an unrepentant heart. Like Jehu and Shallum, their time was limited. We can take heed of this warning as well because the same thing will come in the last days. These armies of self-reliance will defeated in the final battle and it won't even be much of a battle (see Revelation 20).