For if these things be in you,.... Are wrought in you by the Spirit of God, and exercised and performed by his assistance, who works in his people both to will and do:and abound; increase in their acts and exercises by the frequent performance of them: they make you; both by way of influence and evidence,[that ye shall] neither [be] barren nor unfruitful in the knowledge of our Lord Jesus Christ.
There is a knowledge of Christ which is barren and fruitless; and those that have it are so in their conversations, and it will be of no avail to them another day: and this is a mere notional and speculative knowledge, such as is not attended with any inward experience and application of Christ to themselves, or any fruits of righteousness in their lives, and is a bare theory of things relating to his person, offices, and works; but there is a knowledge of him that is spiritual and experimental, by which a soul not only approves of Christ, but places its trust and confidence in him, and appropriates him to himself, and practically observes his commands and ordinances in the faith of him; and in love to him he performs the above duties, and exercises the above graces; from whence it appears, that he is neither barren nor unfruitful himself in the profession of his knowledge of Christ; "or in the acknowledgment of him", as it may be rendered; nor is that a vain, empty, and useless thing: he is not like the barren fig tree, or the earth that bears briers and thorns, and is nigh to cursing and burning, but like a tree planted by a river of water, and is green, flourishing, and fruitful.