Hashem gave us 613 mitzvos, but how can anyone observe them all? Many mitzvos are addressed specifically to kohanim; especially in this bitter exile we are unable to observe all the mitzvos that relate to Eretz Yisroel, and since we have no Beis HaMikdash we cannot fulfill the mitzvos of bringing sacrifices. However, if we love one another and are united we all share in each other's mitzvos and the Torah each of us has studied. The Gemara states that engrossing yourself in the laws of the sacrifices is tantamount to bringing a sacrifice, and studing the construction of the Mishkan is equivalent to taking part in the building of the Beis HaMikdash. Thus if your heart leans towards studying Kodashim and someone else is attracted to studying Moed, both of you share in each other's studies. Similarly, one person is more meticulous is observing one mitzvah, and another is more scrupulous in another mitzvah, yet each is included in the observance of the other in perfect unity. When Jews are united and love one another then Hashem pays each the reward of observing the entire Torah.