1 John 2:3

And hereby we do know that we know him
Either the Father, with whom Christ is an advocate; not as the God of nature, and by the light of it, nor as the lawgiver and Judge of the whole earth, and by the law of Moses; but as the God of all grace, as a God pardoning iniquity, transgression, and sin, as the Father of Christ, and as in him by the Gospel; and this not in a mere notional and speculative way, but with love and affection; not with fear and trembling, as devils know him, nor in theory, as formal professors and hypocrites, but with a knowledge, joined with hearty love of him, and cheerful obedience to him: or else Christ, the advocate and propitiation for sin; and him also, not with a mere notional knowledge of his person and offices, which carnal men and devils themselves have of him, but with that which is spiritual, special, and saving, being from the Spirit and grace of God; and regards Christ as a Saviour, as a propitiatory sacrifice for sin, and an advocate with God the Father; and by which he is approved as such, to the rejection of all other savours, sacrifices, and advocates; and is trusted, confided, and believed in as such, and affectionately loved, and that above all others, in sincerity and truth; and is readily obeyed in his word and ordinances; for where there is true knowledge of Christ, there is faith in him; and where there is faith in him, there is love to him, for faith works by love; and where there is love to him, there will be an observance of his commands; and this is here made the evidence of the true knowledge of him: for it follows,

if we keep his commandments;
not the commandments of men, for the keeping of them arises from ignorance of God, and is a proof of it; nor the commandments of the ceremonial law, which are abolished, particularly circumcision, which is opposed to the keeping of the commandments of God, ( 1 Corinthians 7:19 ) ; but either those of the moral law, and which are more particularly the commandments of God the Father; the observance of which, though it cannot be with perfection, yet being in faith, and from love to God, and with a view to his glory, is an evidence of the true knowledge of him and of his will: or else those commandments, which are more especially the commandments of Christ Jesus; such as the ordinances of baptism and the Lord's supper, which are peculiar to the Gospel dispensation; and which being kept as they were delivered by Christ, and in his name and strength, and to his glory, without depending on them for life and salvation, is an argument and proof of the right knowledge of him; and particularly his new commandment of loving one another may be chiefly designed, that being what the apostle has greatly in view throughout this epistle; now let it be observed, that keeping of the commands of God, or Christ, is not the knowledge of either of them itself, for much may be done in an external way, yet neither God nor Christ be spiritually and savingly known; nor is it the cause of such knowledge, for that is owing to the Spirit and grace of God; but is an effect or consequence of spiritual knowledge, and so an evidence of it; hereby is not the knowledge itself, but the knowledge of that knowledge, that is, that it is true and genuine.