The exhortation to love one another is grounded on the purification of the believer; this purification is a result of their obedience to the truth, and in turn results in a sincere love for fellow believers. The Good News Translation has rearranged the order in the Greek according to the above logical sequence.
The transitional phrase Now that may express a cause for the imperative which follows, namely, love one another, for example, “since you now have love for one another.” One may also express the transition as “in view of the fact that now you have love for one another.”
The truth is only used once in this letter, and probably is equivalent to the gospel (as in 1 Thes 2.10, 12, 13), that is, the Good News of what God has done in Jesus Christ. It is further elaborated in verse 23 by the expression the living and eternal word of God. A proper translation of the truth then, would be “the true teaching from God” or “the true teaching about Jesus Christ” or “the true words about Jesus Christ” or “the teaching about Jesus Christ which is true.”
Obedience refers not to a continuing attitude, but to actual action, that is, acting in accordance with the truth. This is quite clearly the intention: truth leads to the purification of the believer.
Your obedience to the truth may be rendered as “your doing what the truth about Jesus Christ says you should do.”
You have purified yourselves is literally “having purified your souls,” but as in 1.9, “soul” here denotes the whole person, and many translations render it accordingly (for example, New International Version, New American Bible, Die Bibel im heutigen Deutsch “You have become pure”). The word used for purified (Greek agnizō) is used of ceremonial purification in the Old Testament (for example, of objects, Num 31.23; or of people, Exo 19.10), but in the New Testament has come to refer to moral and spiritual purification (for example, James 4.8; 1 John 3.3). In the light of 1.2, “purification” here should probably be understood as moral cleansing, that is, deliverance from the power of sin. The perfect participle refers to an act in the past which remains effective to the present, and accordingly, many scholars see in this a reference to baptism.
It may be important in some languages to translate you have purified yourselves in a negative fashion, for example, “you have become no longer contaminated by sin” or “you have gotten rid of the sin that spoiled you.”
Purification leads to sincere love for fellow believers. Literally, the expression used here is “sincere brotherly love,” which was formerly used to refer to the love between actual brothers and sisters. In the New Testament, however, “brothers” has come to mean fellow believers. The adjective sincere means negatively, free from hypocrisy or deceit, and positively, “genuine” (Phillips, Barclay), a love that comes directly from the heart. To have a sincere love for your fellow believers may be rendered as “to really love your fellow believers.” Such fellow believers may be rendered as “those who believe even as you do.”
After laying the groundwork, Peter moves on to the imperative: love one another earnestly with all your heart. The exhortation to love one another already appears in 1.17 and will be mentioned again in 3.8 and 4.8. Earnestly appears again in 4.8, and in both instances contains the elements of steadiness, ferventness and constancy (compare New International Version “deeply”). Taken as a whole, to love earnestly with all your heart is to involve the whole being in the task of fervently and constantly loving others.
It may be somewhat difficult to provide a satisfactory contrast between the two statements have come to have a sincere love for your fellow believers and love one another earnestly with all your heart. The latter expression should of course indicate an even more intense degree of love. Love one another earnestly may be expressed as “love one another indeed very much,” but the phrase with all your heart must in some languages be translated figuratively with some other organ of the body, for example, “love with all your abdomen” or “love with all your liver.”
Quoted with permission from Arichea, Daniel C. and Nida, Eugene A. A Handbook on The First Letter from Peter. (UBS Handbook Series). New York: UBS, 1980. For this and other handbooks for translators see here .