I am the vine, ye are the branches: He that abideth in me, and I in him, the same bringeth forth much fruit; for without me ye can do nothing.  John 15:5
Jesus spoke these words to His disciples during the Last Supper, which He ate with them on the night of His arrest. He knew they would need to be firmly attached to Him as the Vine in order to weather the crisis of His forthcoming execution and death. 
The imagery that Jesus used was that of a grapevine. This domestic vine has one main stem with several smaller shoots or runners branching off in all directions. These smaller branches owe their lives to the main stem. They could not live apart from the big vine that is rooted in the ground. In the same way, Jesus’ disciples were to stay attached to Him as their Lord and Savior. He as the Vine would sustain and nourish them so they would bear “much fruit” in the days ahead. 
The fruit that Jesus mentions probably refers to the witness that they would bear for Him after His resurrection and ascension to God the Father. Most of these disciples, His “branches,” abandoned Jesus when He was arrested and executed on the cross (see Matthew 26:56). But after His resurrection, they regained their courage and continued the work that Jesus had trained them to do.
In the Old Testament, the nation of Israel was often referred to as a vine (see Psalm 80:8; Isaiah 5:2). But the people fell into sin and idolatry, becoming an empty vine that bore no fruit for the Lord (see Hosea 10:1). Jesus, therefore, has become the True Vine (see John 15:1) whom God has sent to bring salvation to His people.