Of course, Paul is not introducing a new idea here. Jesus himself, when asked which was the greatest commandment, responded by saying that it was to love God and that the second was to love one's neighbor. This not only shows that Jesus believed that Torah could be summed up into these two commands. It also demonstrates that the religious authorities of the time considered this to be at least a likely possibility as well (otherwise, why would Jesus have been asked the question in the first place?). This is further substantiated by other Jewish Rabbinical writings that have been found which provide an assessment of the Torah very similar to Jesus' own response.
Paul then says that the believers should do this "knowing the time". Paul is reworking another theme from the previous chapter; that of the new age. The Church is to be a community shaped by the law of love rather than Torah precisely because of the time in history, the new age has begun through the arrival of the Messiah. Therefore, Paul reminds the church at Rome that the "night" or the old age is coming to an end and the "day" or the new age is dawning. This is an extremely apt metaphor for describing Paul's overlap of the ages in which the believers (and the Church today) live. This is because daylight does not come all at once. Instead, the darkness of night is slowly overtaken by the rising sunlight. So also the establishment of Christ's kingdom is not immediate like someone flipping the light switch in a room. Instead, the inauguration of this kingdom is followed by a substantial amount of time in which the old darkness and the new light intermingle to such an extent that it is not clear where one ends and the other begins although it is absolutely clear that something new and remarkable, something entirely in contrast with the darkness is invading the night sky. Eventually the light will prevail and expose all that the darkness covered but for now the light and darkness exist inseparably along side of one another.
Paul closes this passages by spelling out some specifics of what it means to live "knowing the time". He mentions specifically things like drunkenness, sexual immorality, strife, and jealousy. It is quite possible that Paul chooses these specifics acts because they would have actually been associated with night time and would therefore serve to extend the metaphor of darkness that he has utilized. However, it is also worth noting that these are activities that very much involved the body. Perhaps, Paul is awakening yet another theme from the previous chapter; that of offering our bodies as living sacrifices. Either way, Paul clearly believes that Christian love is not just a warm feeling of friendliness or mere sentiment. Christian love is demonstrated by concrete, physical actions that we do (or in some cases don't do) with our bodies. This is a substantial contrast to our own culture in which love is often thought of as nothing more than emotion or sexual desire. Simultaneously, it seems our culture is questioning more and more how the "religious" or "spiritual" has anything to do with what we do to our bodies or the bodies of others as long as no one gets hurt. This passage of Scripture is a challenge for the Church to reclaim the connection between the physical and the spiritual and thereby to reclaim an embodied and therefore Christian understanding of what it means to love.