Devarim, 5:7: “You shall not recognize other gods in My Presence”.
Devarim, 6:4: “Hear, Israel, HaShem is our G-d, HaShem in the One and Only.”
Two of the most well-known passages in the Torah appear in Parshas Va’eschanan: The Ten Commandments and the Shema. On close analysis, there seems to be a repetition between two of the Mitzos that feature in these passages. The second of the Ten Commandments is the Prohibition to follow other gods (elohim acheirim), and the Shema itself is the Mitzva to believe that G-d is the one and only G-d, (Yichud HaShem), which indicates that it is forbidden to believe in many gods. This Prohibition seems to have been already covered in the Mitzva not to follow other gods, so what is added by the Mitzva to believe that there is only one G-d?
Evidently, the Mitzva of Yichud HaShem goes a lot further than just the requirement to believe that there is only one G-d. In order to fully understand this Mitzva and contrast it to the Mitzva of elohim acheirim it is first necessary to explain what it means not to follow other gods and how this applies nowadays. In earlier times, there was a widespread desire to actively worship false gods so this Mitzva was highly pertinent. However, from the time that the Anshei Knesses HaGedolah removed the inclination of Avoda Zara, it would appear that this Mitzva is basically obsolete, so how does it apply to us.
However, in truth, the idea behind this Mitzva is highly pertinent at all times. A false god is not just a physical idol, rather it is anything that a person ascribes power to, meaning that he believes that this thing is the source of a person’s success. It can include money, desires, oneself, one’s boss, or any number of other things that a person feels are the key to his success in life.
The Gemara points out another false god that influences everyone. David HaMelech in Tehillim states that “there should not be within you a strange god”. The Gemara explains that this strange god refers to the yetser hara that actually pervades a person’s very consciousness. One possible meaning of this is that the yetser hara itself is what controls a person’s drives and fulfilling its desires will provide a person with satisfaction. And in this form, it is a kind of false god.
Thus, the Mitzva not to have other gods tells us that all those forces that convince us that the way to succeed is through them, are null and void when contrasted to the all-powerful G-d. Yet, there is still something lacking in what a person’s attitude should be towards the various sources of power outside of G-d – that is where the Mitzva of Yichud HaShem steps in: Yichud HaShem teaches that, in truth, all of these powers are not ‘fighting’ HaShem, they are not against Him. Rather, in truth, they are part of HaShem’s purpose just like everything in Creation. For example, the ultimate goal of the yetser hara is not, chas v’Shalom, to cause us to turn from HaShem, rather its goal is for us to overcome its temptations and thereby become closer to Him. This is why Chazal state that when G-d saw that the creation on the sixth day was ‘very good’ in contrast to the other days where it was merely ‘good’, He was referring to the creation of the yetser hara – it is indeed very good because it brings us closer to our purpose of coming closer to HaShem by overcoming its challenges. So too, the other powers that we view as taking away from closeness to HaShem are also tools to get closer to Him.
In this vein, another application of Yichud HaShem is that everything that happens to a person is directed at the same purpose of bringing him closer to HaShem. Thus, seemingly ‘bad’ events that take place come from HaShem just as must as pleasant Hashgacha. Both are there to bring us closer to him, albeit in different ways. My Rebbe, Rav Yitzchak Berkovits shlit’a expresses this even regard to ‘minor’ suffering that we view as nuisances. In his words:
“We say that some things are good and some things are bad. What are you talking about? That negates “Hashem Elokeinu Hashem Echad!” You mean some things are working in one direction and some things in the other direction? Everything was created for the same purpose, because it has the same source, and its source is only good! Everything is made up of this Hashem-liness. Everything is good. Everything is created only for the sake of bringing us back to being misdabek b’HaShem, being one with HaShem, and taking pleasure in it! Oh, I’d really want to learn, but I keep getting these problems in life. I really want to learn but I caught a cold, what a nuisance. It’s standing in the way of my Avodas HaShem. Baloney! You mean there’s something other than nature that is there for the sake of bringing you to eternal pleasure? You mean this cold is a nuisance that came in from Mars, it came from another sphere? This cold was created to bring you closer to Hashem no less than anything – than your siddur and your gemara and your chumash. It is just that there are lots of different aspects of our growth. There are many different things we have to learn, and there are some things you can only learn when you have a cold. Now go figure out what that was for. Absolutely everything is pointing in the same direction. Everything has the same purpose. There’s total unity in everything. There are no other forces. There’s no evil. It’s illusion! We’re misunderstanding it, because we take it seriously. We think it’s really, really evil. It’s not.”
Thus, Yichud HaShem builds on elohim acheirim and tells us that as well as viewing these perceived sources of success in our lives as null and void against HaShem, we should actually look at them as helping us get close to HaShem. May we all succeed in fulfilling both of these seminal Mitzvos in the ideal fashion.
 Shabbos, 105b.
 Tehillim, 81:10.
 From a Shiur on the Six Constant Mitzvos.