We come now more into the design and substance of the epistle; and here we have,
I. The apostle's request: Now, I beseech thee, lady. Considering what it is that he entreats, the way of address is very remarkable; it is not any particular boon or bounty to himself, but common duty and observance of divine command. Here he might command or charge; but harsher measures are worse than needless where milder will prevail; and the apostolical spirit is, of all other, the most tender and endearing. Whether out of deference to her ladyship, or apostolical meekness, or both, he condescends to beseech: And now I beseech thee, lady. He may be supposed speaking as another apostle does to a certain master to whom he writes: Wherefore, though I might be very bold in Christ (and according to the power with which Christ hath entrusted me) to enjoin thee that which is convenient, yet, for love's sake I rather beseech thee, being such a one as the aged, the elder. Love will avail where authority will not; and we may often see that the more authority is urged the more it is slighted. The apostolical minister will love and beseech his friends into their duty.
II. The thing requested of the lady and her children - Christian sacred love: That we love one another, Jo2 1:5. Those that are eminent in any Christian virtue have yet room to grow therein. But, as touching brotherly love, you need not that I write unto you; for you yourselves are taught of God to love one another. But we beseech you, brethren (and sisters), that you increase more and more, Th1 4:9, Th1 4:10.
1. This love is recommended, (1.) From the obligation thereto - the commandment. Divine command should sway our mind and heart. (2.) From the antiquity of the obligation: Not as though I wrote a new commandment unto thee, but that which we had from the beginning, Jo2 1:5. This commandment of mutual Christian love may be said to be a new one in respect of its new enaction and sanction by the Lord Christ; but yet, as to the matter of it (mutual holy love), it is as old as natural, Jewish, or Christian religion. This commandment must every where attend Christianity, that the disciples of it must love one another.
2. Then this love is illustrated from the fruitful nature of it: And this is love, that we walk after his commandments, Jo2 1:5. This is the test of our love to God, our obedience to him. This is love to ourselves, to our own souls, that we walk in obedience to divine commands. In keeping them there is great reward. This is love to one another, to engage one another to walk in holiness; and this is the evidence of our sincere, mutual, Christian love - that we (in other things) walk after God's commands. There may be mutual love that is not religious and Christian; but we know ours to be so, by our attendance to all other commands besides that of mutual love. Universal obedience is the proof of the goodness and sincerity of Christian virtues; and those that aim at all Christian obedience will be sure to attend to Christian love. This is a fundamental duty in the gospel-charter: This is the commandment, that, as you have heard from the beginning, you should walk in it (Jo2 1:6), that is, walk in this love. The foresight of the decay of this love, as well as of other apostasy, might engage the apostle to inculcate this duty, and this primordial command, the more frequently, the more earnestly.

And this is love - That is, our love is shown and proved by our walking according to the commandments of God; for love is the principle of obedience.

And this is love, that we walk after his commandments,.... By observing them as a rule of conversation, in so doing love is shown to God; and such may expect the fresh discoveries of the love of God to, them; See Gill on Jo1 5:3;

this is the commandment, that as ye have heard from the beginning,

ye should walk in it; that is, this is the will of God, that his people should walk in the truth of the Gospel, and abide by it, as they heard and received it at their first conversion, from the mouths of the apostles, or other faithful ministers of the word; a reason for which, is given in Jo2 1:7.

"Love is the fulfilling of the law" (Rom 13:10), and the fulfilling of the law is the sure test of love.

This is the commandment--Greek, "The commandment is this," namely, love, in which all God's other commandments are summed up.