How can you see a thought, an intention, or the integrity of someone’s words? It’s obvious you can’t see these things themselves. However, what you can see are the effects of these in the deeds of those possessing them. Scripture points us to this truth and far beyond when it says:
If anyone says, “I love God,” and hates his brother, he is a liar; for he who does not love his brother whom he has seen cannot love God whom he has not seen. 1 John 4:20 English Standard Version (ESV)
[Earlier, the Apostle John] said, “He gave us commandment that we should love one another.” How [can you] be said to love Him whose commandment [you hate]? Who shall say, I love the emperor, but I hate his laws? In this the emperor understands whether [you] love him, that his laws be observed throughout the provinces.
Our Emperor’s [i.e., Christ’s] law, what is it? “A new commandment give I unto you, that you love one another.” [You say] then, that [you love] Christ: keep His commandment, and love thy brother. But if [you] love not [your] brother, how [can you] be said to love Him whose commandment [you despise]?
…The real reason which makes [our] obedience to [the command to love one another] difficult is the slackness of our own hold on the Centre. In the measure in which we are filled with Jesus Christ, in that measure will that expression of His spirit and His life become natural to us.
Every Christian has affinities with every other Christian, in the depths of his being, [in such manner] that he is a great deal more like his brother, who is possessor of ‘like precious faith,’ however unlike the two may be in outlook, in [distinctive habits], and culture and in creed, than he is to another man with whom he may have a far closer sympathy in all these matters than he has with the brother in question, but from whom he is parted by this, that the one trusts and loves and obeys Jesus Christ, and the other does not.
So, for individuals and for churches, the commandment takes this shape—Go down to the depths and you will find that you are closer to the Christian man or community which seems furthest from you, than you are to the non-Christian who seems nearest to you. Therefore, let your love follow your kinship, and your heart recognize the oneness that knits you together.
That is a revolutionary commandment; what would become of our present organizations of Christianity if it were obeyed?
That is a revolutionary commandment; what would become of our individual relations to the whole family who, in every place, and in many tongues, and with many creeds, call on Jesus as on their Lord, their Lord and ours, if it were obeyed?
I leave you to answer the question. Only I say the commandment has for its [primary] scope all who, in every place, love the Lord Jesus Christ…
Note that MacLaren’s comments were directed toward this verse:
A new commandment I give to you, that you love one another: just as I have loved you, you also are to love one another. By this all people will know that you are my disciples, if you have love for one another.” John 13:34-35 (ESV)
Here we see again that Christ directs us to make the invisible (i.e., our following Him) visible to the world through our deeds of heartfelt sacrificial love towards one another. Let us act accordingly.