For I know the plans I have for you, declares the Lord, plans for welfare and not for evil, to give you a future and a hope. (Jer. 29:11)
These are the words of the letter that Jeremiah the prophet sent from Jerusalem to the surviving elders of the exiles, and to the priests, the prophets, and all the people, whom Nebuchadnezzar had taken into exile from Jerusalem to Babylon. ... “For thus says the Lord: When seventy years are completed for Babylon, I will visit you, and I will fulfill to you my promise and bring you back to this place. For I know the plans I have for you, declares the Lord, plans for welfare and not for evil, to give you a future and a hope. Then you will call upon me and come and pray to me, and I will hear you. You will seek me and find me, when you seek me with all your heart. I will be found by you, declares the Lord, and I will restore your fortunes and gather you from all the nations and all the places where I have driven you, declares the Lord, and I will bring you back to the place from which I sent you into exile. (Jer. 29:1, 10-14)
Jer. 29:11 has been used as a prooftext for so long, to indicate God's blessings to be with the person addressed, that it may seem strange to indicate that it has been often misquoted. In fact, precisely because it is used and abused so often that when its abuse is pointed out, those who do so seem strange and even wrong. However, reading it in context would show us the true meaning of this verse, and the glaring error in utilizing it as a general text of blessing.
The first thing we can and must see immediately is that it is addressed to Israel. It is not addressed to everyone in general but to the people of God in the Old Testament. Therefore, Jer. 29:11 cannot be a general blessing formula to be indiscriminately given to all, but only applicable to God's people.
Logically, we can see God's purposes of judgment on the wicked (Prov. 16:4) and his judgments on various nations and peoples throughout history. Can we say that there is a general blessing: that God has a good plan for all people? Not unless we believe in a God whose plans can be frustrated, contrary to the express teachings of Scripture in this regard (Ps. 115:3, Dan. 4:35).
The context of Jer. 29:11 is Jeremiah's address to the Israelite exiles in the country of Babylon. God has judged Judah for her wickedness, and sent King Nebuchadnezzar and the Babylonians to eliminate Judah as judgment for her wickedness. The exiles are in severe hardship in their captivity in this hostile land, and it is in this situation that Jeremiah addresses the people.
The promise of God's blessing and favor upon the exiles in verse 11 thus comes in the midst of severe hardship, and thus is meant to comfort God's people of God's love and favor which is still upon them. Yet from this, we can immediately see that it is an untruth that God's people will not suffer merely because we are His. God indeed has a wondrous plan for His people, but that does not preclude suffering, as the life of Job demonstrates.
In conclusion, Jer. 29:11 is a verse of comfort to Christians, especially to those in affliction, that God has a plan for them for their good. It is however not for those who do not believe in Christ, and neither is it a verse to promote the health-and-wealth heresy, as this promise does not preclude suffering in this life.