Abiding in Christ means learning dependence on Christ (John15:4)

To be fruitful (i.e., to grow and abound) spiritually, you must be dependent on the vine, which v. 1 identifies as Christ. This dependence is “continuous dependence on the vine, constant reliance upon him, persistent spiritual imbibing of his life” (D. A. Carson, John PNTC 516).

Augustine wrote, “They are not in him in the same kind of way that he is in them. And yet both ways tend to their advantage, not to his. For the relation of the branches to the vine is such that they contribute nothing to the vine but derive their own means of life from it, while that of the vine to the branches is such that it supplies their vital nourishment and receives nothing from them. And so their having Christ abiding in them and abiding themselves in Christ are in both respects advantageous not to Christ but to the disciples. For when the branch is cut off, another may spring up from the living root. But that which is cut off cannot live apart from the root.” (Ancient Christian Commentary on Scripture, IVb:166)