Jeremiah has a largely negative message for the people of God. In short, that message is: “You have disobeyed God. You have turned away from the Lord to idols that are not God. Therefore, the Lord is going to punish you by sending you into exile in Babylon.”
Yet, in the midst of all these discouraging words of judgment, there are a few gems of encouragement and beauty. One of these is found in Jeremiah 17:7-8,
Blessed are those who trust in the Lord,
whose trust is the Lord.
They shall be like a tree planted by water,
sending out its roots by the stream.
It shall not fear when heat comes,
and its leaves shall stay green;
in the year of drought it is not anxious,
and it does not cease to bear fruit.
These verses are reminiscent of Psalm 1. However, here the key to becoming like a tree planted by water is not delighting in the law of the Lord, but simply trusting in the Lord.
Of course, we all have a hard time trusting in the Lord. It does not matter how long we have been trying to follow God. There will come times, even late in life, when we find it hard to trust God, no matter how many times he has come through for us before. I suppose this is true because we are weak, sinful, human beings.
Therefore, what do we do when we have trouble trusting in the Lord, but we want to trust, we want to believe? It seems to me that the only solution, the only authentic and right response on our part, is to pray something like the father who brought his demon-possessed son to Jesus: “I believe; help my unbelief!” (Mark 9:24)
I believe that Jesus will always respond positively to a humble prayer like that and he will do for us what we need, just as he healed the son of that desperate father.