Jesus said to his disciples: "A good tree does not bear rotten fruit, nor does a rotten tree bear good fruit. For every tree is known by its own fruit. For people do not pick figs from thornbushes, nor do they gather grapes from brambles. A good person out of the store of goodness in his heart produces good, but an evil person out of a store of evil produces evil; for from the fullness of the heart the mouth speaks.” -Luke 6:43-45
You can tell a tree by its roots. If we examine the roots of a tree, even if overgrown by weeds and vines, at its foundation, we still see the tree is born from the Tree of Life, not the scrub brush that surrounds it. One is from God, and the other is from the enemy. Only the Tree of Life produces the shoots that make good fruit. The thornbush tries to overgrow the fruit tree to keep it from bearing good fruit. But by allowing Christ into our hearts, we allow Him to prune away the brambles so that the good fruit God intended, may grow.