The individual instructions or commands in Scripture, such as Romans 13:8-10 can stand alone and preach very well.  Sermons more accurately teach those commands, however, when the command “to love each other”, for instance, is explained in light of the teaching which started the list of instructions.  So, in the case of loving each other, this is all part of discerning “the will of God” or a part of how the “renewed mind” of the Christian lives life or a part of being “transformed” or a part of not being “conformed to this world” (all taken from Romans 13:2).  Or, we could say that the individual commandment of Romans 13:8 is one thing that happens when Christians present their “bodies as a living sacrifice…to God” (cf. Romans 13:1).  Loving each other is simply one of many ways in which the Christian life is lived out.  In this sense, although the instruction can stand alone, it’s clearer and maybe more accurate to place the instruction into the immediate context and allow that context–whichever part above you choose–to be the base or foundation for the individual commandment.