לזכות ידיד נפשי יעקב יחזקאל בן חנה מאשא
[תהילים ב, ח]
But in my heart you put gladness from when their grain and wine abounded.
This can mean that I am happier because of my faith in Hashem [as he expresses in the next pasuk] than the farmers are when they have an abundant crop [Daas Mikra].
The Toldos Yaakov Yosef [Talmid Habaal Shem Tov Parshas Re'eh ד"ה זש"ה] explains that while the rest of the world is rejoicing in their gashmiyus - grain and wine - I am joyful with the שכינה. [The word לב is a reference to the שכינה according to the Zohar Hakadosh quoted in the footnote there. This לב is also referred to in the pasuk וטוב לב משתה תמיד].
The Sfas Emes [סוכות תרמ"ג] explains that the Gentiles are happy with the חיצוניות ההשפעה - the abundant crop, but I am only interested in the פנימיות - the simcha that is in the heart. [The Medrash says that this simcha is חכמה. See Zeev Yitrof Tehillim 2, Chapter 30 and 95. ]. This occurs at Succos time which is the time when the השפעות come down for חג האסיף - the holiday of gathering in the crop.
Others understand that Dovid Hamelech was so happy because when he saw how much the Goyim benefited, he was assured that ultimately Klal Yisrael would receive many times more.
Rav Charlap teaches based on the previous pasuk רבים אומרים מי יראנו טוב - many people wonder when they will experience good. But they are not concerned with glorifying the Name Of Hashem. Therefore, they harbor hopes that others should fail and thereby they will have success.
I am not like that. My primary concern is that Hashem's name should be glorified so I am thrilled when others, even my enemies, have success. However, this feeling of joy that permeates my being is not my own doing but rather a gift from Hashem. נתתה שמחה בלבי - YOU put joy in my heart, מעת דגנם ותירושם רבו - From when their grain and wine abounded.
From this we learn the importance of having an עין טובה - a positive view of the good fortune of others.
Here is the language of Rav Charlap ztz"l:
If I may add a suggested explanation: We think that if we would just have financial success we would be really happy. That is where it is at. But when you see others who are making so much money and aren't happy you realize that what really matters is Avodas Hashem. THAT is the source of true happiness. נתתה שמחה בלבי - You put gladness in my heart, from the time of their bumper crop. מעת דגנם ותירושם רבו - And then I realized that just having a good crop is not going to give me true happiness.