2 John 1:5-6
And now I beseech thee, lady, not as though I wrote a new commandment unto thee, but that which we had from the beginning, that we love one another. And this is love, that we walk after his commandments. This is the commandment, That, as ye have heard from the beginning, ye should walk in it.
Leviticus 19:18
Thou shalt not avenge, nor bear any grudge against the children of thy people, but thou shalt love thy neighbour as thyself: I am the LORD.
John's explicit declaration that he writes no new commandment but the one received from the beginning establishes the love statute as a Mosaic constitutional provision, not an apostolic innovation. The neighbor-love ordinance of Leviticus 19:18 is precisely 'that which we had from the beginning' — the love commandment predates the new covenant by the entire Mosaic period. John's insistence on the commandment's antiquity is a deliberate statutory citation: the directive to love one another is the Levitical ordinance operating in its new covenant application, unchanged in substance from the moment Moses declared it.
2 John 1:6
And this is love, that we walk after his commandments. This is the commandment, That, as ye have heard from the beginning, ye should walk in it.
Deuteronomy 5:10
And shewing mercy unto thousands of them that love me and keep my commandments.
John's definition of love as walking after the commandments is the inverse of the Deuteronomic covenant structure: Deuteronomy 5:10 links love for God directly to commandment-keeping, establishing that the two are constitutionally inseparable. John articulates the same structural inseparability from the love side: love is not a sentiment but a walk — a sustained pattern of commandment-following. The Deuteronomic statute that reserves mercy for those who love God and keep his commandments provides the constitutional framework within which John's definition of love as commandment-walking operates.