The prominent place the Symposium holds in our canon comes as much as a result of its literary merit as its philosophical merit. While other works among Plato's middle-period dialogues, such as the Republic and the Phaedo, contain more philosophical meat, more closely examining the Theory of Forms and intensely cross-examining interlocutors, none can match the dramatic force of the Symposium. It is lively and entertaining, with sharp and witty characterization that gives us valuable insight into the social life of Athenian intellectual circles.
From a philosophical standpoint, the Symposium is also far from bankrupt. Not only does it give us some insight into the Theory of Forms in Diotima's discussion of the Form of Beauty, but it also gives us a number of varying perspectives on love. Significantly, we see Plato rejecting the romanticization of sexual love, valuing above all an asexual and all-consuming passion for wisdom and beauty. Ultimately, he concludes, the philosopher's search for wisdom is the most valuable of all pursuits. In the Symposium, Plato values philosophy, as exemplified by Socrates, over a number of other arts which are given as points of comparison: medicine, as exemplified by Eryximachus, comedy as exemplified by Aristophanes, and tragedy as exemplified by Agathon.
The series of speeches in praise of Love are not simply meant as beating around the bush that leads up to the main event. They mirror Diotima's discussion of the mysteries, where she suggests that one can approach the truth only through a slow and careful ascent. Similarly, we can see each speech, with a few exceptions, as coming closer and closer to the truth. This suggestion is reinforced by the fact that Socrates alludes to all the foregoing speeches in his own speech, as if to suggest that his words could not be spoken until everyone else had said their piece. This staggered approach to truth is also reflected in the framing of the narrative, whereby we are only able to gain access to this story through a series of narrative filters.
We should note that Socrates is the exemplar of the lover of wisdom and the lover of beauty, but is neither wise nor beautiful himself. In this way, he best represents Love, which Diotima describes as a mediating spirit that moves between gods and men. Love himself never has anything, but is always desirous of happiness, beauty, and wisdom. The same is true with Socrates. Those who follow his lead will not necessarily attain wisdom, but will find fulfillment in a life-long pursuit of wisdom. The state of having attained wisdom is represented by Diotima, not Socrates, and she speaks through Socrates as a god-like and unapproachable figure.
There is also some discussion as to exactly what is being discussed in the Symposium. The Greek word eros leaves the matter ambiguous as to whether we are discussing love in the normal, human, sense of the word, or if we are discussing desire in a much broader sense. The later speeches in particular tend toward this broader interpretation. Diotima gives what is perhaps a satisfactory answer by suggesting that, while all kinds of desire might be considered love, we normally restrict use of that term to one particular kind of desire, the desire that exists between two human beings.
Philosophy aside, however, the Symposium still makes a terrific read. Aristophanes' myth is delightful, Alcibiades' drunken antics are entertaining, and the whole narrative shimmers with life. We also get a very clear sense of the dynamics of sexual attraction and courtship--both male-male and male-female--in ancient Athens, and we are given a beautiful portrait of one of the high-points of the Athenian scene: the symposium.
You do not have to look outside you as everything is in your "self", everybody is the two energies (woman-man/yin-yang/...) and if you awaken your "opposite" you are "one", you are realized, totally happy. This is called e.g. in the Bible the Holy or Mystic Marriage. Also the alchemists describe it as "Coniunctio Oppositorum", the Philosopher's Stone, make Gold from Lead,... See the writings of the Mystics too. Etc.