You either feel love or you don't. How can it be a commandment?
This sentence calls loving other people a "positive commandment." That means a "do" on the Torah's list. The Gemara counts 248 of those, next to 365 "do nots." But nobody can switch on a feeling because they were told to.
The Ramban (Nachmanides, a leading Torah commentator in 13th-century Spain) says so directly. "As yourself" is an overstatement, because the human heart cannot take on loving someone else the way it loves itself. He adds a proof from Rabbi Akiva, who called this same verse a great principle. Two people are traveling with one flask of water, enough to keep only one alive. Rabbi Akiva ruled: your own life comes first.
So what is commanded? The Ramban suggests an answer from the wording. The verse says "love to your fellow," not "love your fellow." Want for him every good thing you want for yourself: money, honor, knowledge. And want it without the usual quiet condition, "as long as I have more than he does." That jealousy is what the verse comes to remove. His example is Yonatan, the son of King Shaul, who could say to David: "You will be king over Israel."
The Rambam (Maimonides) turns it into things a person can do. Speak well of other people. Care about their money and their honor the way you care about your own. Elsewhere he gives a simple test: whatever you would want others to do for you, do for them. That is why, he says, visiting the sick and comforting mourners are part of this mitzvah.
The two do not put the weight in the same place. In his list of the commandments the Rambam does describe a feeling: love and compassion for your brother like what you have for yourself. The Ramban says the heart cannot do that. Both spell the mitzvah out as what you want for people and how you treat them.
The sentence in this siddur is worded the same way. It does not report a feeling. It says: I accept this commandment on myself. That is something a person can decide on any morning.
Ramban on Vayikra 19:18,Bava Metzia 62a,Rambam, Laws of Character Traits 6:3,Rambam, Laws of Mourning 14:1,Rambam, Sefer HaMitzvot, Positive Commandment 206,Makkot 23bDavening is between me and God. Why start with other people?
It looks like the wrong place for this line. You came to talk to God. Nobody else is part of that conversation.
The Arizal, the kabbalist of Tzfat who taught this practice, says they are. He gives a reason. When you accept the mitzvah to love every Jew, your prayer goes up "included with all the prayers of Israel," and then it is able to rise and bear fruit.
The Kitzur Shulchan Aruch (a short guide to daily Jewish law from the 1860s) fills in the logic. If hearts are divided down here, there is no unity above. When people are united, their prayers join together, and a joined prayer is one that God accepts.
You can see the same idea in the wording of the prayers. The Gemara quotes a traveler's prayer in the singular: lead me in peace. The sage Abaye says a person should always include himself with the community, so the prayer should say "lead us." The Amidah (the silent standing prayer) is built the same way. Forgive us. Heal us. Nearly every request in it is in the plural.
The Talmud Yerushalmi (the Gemara of the Land of Israel) has a picture of people who are joined like that. It comes up where the Yerushalmi explains the ban on revenge. A person cutting meat cuts his own hand. He does not hit the hand that held the knife. A classic commentary explains: all Israel is one body. The Arizal's teaching uses the same picture for a group of friends. Each one should see himself as one limb.
So the order makes sense. The main requests in the prayers ahead are worded as "us." This line comes first, so that when you say "us" you have already decided who is in it.
Sha'ar HaKavanot, Morning Blessings,Kitzur Shulchan Aruch 12:2,Berakhot 29b-30a,Talmud Yerushalmi, Nedarim 9:4, with Korban HaEdahWhat about someone who actually hurt me?
The Torah expected the question. "Love your fellow as yourself" does not appear in a passage about people who are easy to like. It closes a short passage about people who wronged you.
The verse before it says: "Do not hate your brother in your heart. Rebuke your fellow." The Rambam (Maimonides) explains what that looks like. When someone wrongs you, do not hate him and stay silent. You are commanded to tell him: why did you do this to me? If he then asks you to forgive him, forgive, and do not be cruel about it. So the first step is not pretending that nothing happened. It is saying it to the person.
Then comes our verse: no revenge, no grudge. The Ramban (Nachmanides) is careful about what that does not cover. If someone owes you money or damaged what is yours, you do not have to let it go. You may take him to court and be paid. The ban is on getting even in everyday favors that nobody owes anybody: I will not lend you mine, because you did not lend me yours.
The Rambam says where it should end. Wipe the matter from your heart, because as long as a person holds on to it and keeps remembering it, he may come to take revenge. He adds a practical reason: this is the attitude that lets people live together and deal with each other.
The examples these sources give for revenge and a grudge are everyday ones, like a tool that was not lent. When the hurt is serious, how this applies is a real question, and one to take to a rav or another adult you trust.
Vayikra 19:17-18,Rambam, Laws of Character Traits 6:6 and 7:8,Ramban on Vayikra 19:18