The Root Produces the Fruit

John 15
⁴ Remain in me, and I will remain in you. For a branch cannot produce fruit if it is severed from the vine, and you cannot be fruitful unless you remain in me.
⁵ “Yes, I am the vine; you are the branches. Those who remain in me, and I in them, will produce much fruit.
¹⁰ When you obey my commandments, you remain in my love
¹² This is my commandment: Love each other in the same way I have loved you.

Summed up;
We bear fruit by being joined to the vine (Jesus).
We are joined to the vine by remaining in Him.
We remain in Him by keeping His commands.
His root commandment is to love.

Therefore, we bear fruit by loving.