In John 15:1-7 we find Jesus delivering a monologue in which he describes a scene common to first-century Palestinians: a vineyard in which a vine is cultivated to produce fruit. Drawing out the analogy, the disciples are branches who draw their life sustenance from their connection to the vine. This image aligns well with the metaphor of Jesus the Life-Giver.  As he continues to explain, those who remain in him will bear much fruit. Inversely, those who are separated from him can do nothing without the life that he provides.
The image is a peaceful one for me. Having some familiarity with raising vegetables in a home garden as a child, this image taps into experiences to which I can readily relate. I am drawn to the organic nature of the image and the idea of maturing and growing into fruition over time. ] The idea of Jesus as a source of life also resonates with my personal spiritual journey. At the same time I remember the damage caused to some of our plants by a storm which broke some branches away form the main body of plants in the garden, resulting in a slow withering and death of the part of the plant that was separated from the root system. I find it easier to connect to this image than to ideas foreign to my cultural context such as a shepherd or a high priest. 
However, this image also has a secondary association for me which is not nearly as pleasant. I once attended a church that suffered the problem of a revolving congregation. Rather than growing larger, it would attract people for a time that would then gradually detach and move away from the church. New people were constantly coming and joining the church for a time, only to leave again for various reasons.  In an attempt to cut attrition, the lead pastor of the church used the image of the Vine and the branches as a metaphor for community life within the Body of Christ, preaching on this passage on Sunday and then covering the passage in John painstakingly, verse by verse, for several weeks in bible study. However, unlike Jesus’ original metaphor, the members were no longer each connected directly to Jesus, the Life-Giver, but rather to the local church community. The implication became that by nature we are called to live in community within the church and anyone who leaves the (local) church will wither and die as though "cut off" from the source of life. Clearly this was not the intent of the original metaphor presented in the gospel of John. 
This image of the Vine suggests a subjective view of the atonement. Rather than overcoming evil forces as in the Classical view or somehow paying a debt as in the Latin view, Jesus is portrayed primarily as the source from which all life is derived. [.] This subjective image of the atonement was first formulated by Peter Abelard in the twelfth century in response to Anselmian satisfaction theory (Placher 131). According to his model the example provided by Jesus (especially in his willingness to die at the hands of human beings on the cross) demonstrates so powerfully for us the love that God has for the world that the natural response on the part of humanity would be to respond in love back to God.  Abelard emphasized Jesus’ role as the Teacher and Example who inspires humanity to love and thereby reconciles fallen humanity to God (Aulén 96).
Applying the subjective theory to the vine metaphor, those who are joined to the Vine and spend their lives in close communion with it are infused with the divine, life-giving nature of Jesus, resulting in a rich, full life that in turn produces much fruit. (Note that the details of the metaphor cannot be pushed too far. In life as we know it, branches do not seek out a vine in hopes of connecting to it to find nourishment. Rather they are an outgrowth from the vine itself.) 
As Aulén points out, the subjective model places no great emphasis on the death of Jesus (96). ] Indeed, the image is purely one of bountiful life that results from being connected to Jesus. Any death seen in the image concerns only those who lose their connection to the Vine. Citing Aulén’s classic work, Marcus Borg places this image of Jesus within the model of a modified story of Exile and Return (128). He explains this particular "macro-story" found in scripture as the image of the Babylonian captivity from 587-539 BCE (125). During this time the Jews were cut off from their homeland (and the central shrine of their devotion to Yahweh, the Temple of Jerusalem), resulting in a sense of loss, stagnation and death as the people mourned as aliens in a foreign land.  Generalizing from this point, the human condition becomes one of estrangement from God in which we suffer from a loss of life and vitality. However, by returning home it is possible to reconnect to the source of love and life and once again flourish and live productive lives.
The metaphor of the Vine is a modified version of this motif, in that it only works in one direction. As long as the branches remain connected to the Vine, they receive all that is necessary to abundant life that produces much fruit. Like the Israelites cut off from their homeland and taken away into captivity, those who are cut off from the Vine shrivel up and die. For the Israelites there was a possibility of return and reconnection with the home, if they survived long enough. However, in the metaphor of the Vine, those who have lost their vital connection with the source of life are thrown away and wither. They are gathered up, cast into the fire and burned. The metaphor does not lend itself to second chances at reconnection. 
The idea of the Vine that functions as the life-giving source works well with orthodox views of the Incarnation. An Ebionitic Jesus would not differ in any substantive way from the branches/people that are connected to him. As such, he would not be able to provide any special life source that they could not achieve on their own.  A Docetic view of Jesus, denying his humanity, would also not work well with this metaphor. In terms of the analogical Vine, Jesus must be made of the same "stuff" as humanity in order for the branches to organically "grow" from the Vine.  No one has seen a supernatural, otherworldly vine from which grow regular earthly branches.
On the other hand, Jesus must be somehow different from the average human being, possessing a source of life that he transmits to others by virtue of their connection to him. Either the Alexandrian model, which focuses on Deity coming down into fleshly form, or the Antiochene model, which focuses on the human aspects of Jesus that rise to the Divine, would meet the criteria for a Vine to which humanity can directly connect for nourishment and growth. 
Aulén, Gustaf. Christus Victor: An historical study of the three main types of the idea of atonement. Trans. A. G. Herbert. Eugene, OR: Wipf & Stock Publishers, 2003.
Borg, Marcus J. Meeting Jesus Again for the First Time: The historical Jesus and the heart of contemporary faith. San Francisco: Harper Collins, 1995.
Placher, William C. Jesus the Savior: The meaning of Jesus Christ for Christian Faith. Louisville, KY: Westminster John Knox Press, 2001.