The person that delights in God’s Torah is like a tree planted by streams of water. Remember that Israel was a more arid land than much of the US (unless you live in Nevada), that was often prone to periods of drought and famine (Gen. 12:10; 43:1; Jer. 14:1).
So, if you wondered why someone would be obsessed by Torah (v. 2), verse 3 answers the question. Torah-obsession directly leads to prosperity, just like a leafy tree by the stream. Everything that this person does prospers.
The thing I love about this psalm is the motivation, that blessings will come to those who focus their lives on God’s word, but it almost sounds too good to be true.
It sounds like a promise of prosperity, almost prosperity-gospel. So, what type of prosperity do you think the psalmist is referring to? What danger is there to making such an open-ended promise of prosperity?