While Jesus did not originate the concept of the God-man relationship as one of love He did give it new emphasis and brought it into sharper perspective. The characteristic Old Testament emphasis is upon obedience, that of the New Testament upon love, yet it remains a commandment, an obligation. It is the chesed, or covenant-love of the Old Testament wedded to the Greek term agapē which emerges as the important word in the Christian ethos. It denotes a discriminating love resulting from choice. The newness consists in the source and nature of this love; it is the supreme criterion of one’s relationship to God (1 John 5:3; cf. Luke 10:27).
Christ’s Love Fulfilled in Death Becomes the Law of the Church
The death of Christ wherein the love of God was exemplified and made manifest as the basis and principle of all spiritual life (Joh 13:34). Paul therefore generalizes all pre-Christian morality as a system of law and commandments, standing in antithesis to the grace and love which are through Jesus Christ Ro 5-7). Believers in Christ felt their experience and inward life to be so changed and new, that it needed a new term (agape = "love") to express their ideal of conduct (see Charity).
Another change that grew upon the Christian consciousness, following from the resurrection and ascension of Christ, was the idea that He was the permanent source of the principle of life. "Jesus is Lord" (1Co 12:3). Hence, in the Johannine writings the principle described by the new term agape is associated with Christ’s lordship and solemnly described as His "new commandment." "A new commandment I give unto you, that ye love one another; even as I have loved you, that ye also love one another" (Joh 13:34). To the Christians of the end of the 1st century it was already an old commandment which they had from the beginning of the Christian teaching (1Jo 2:7; 2Jo 5); but it was also a new commandment which ever came with new force to men who were passing from the darkness of hatred to the light of love (1Jo 2:8-11).