“bear a grudge.” Although almost all English translations have “bear a grudge,” the Hebrew text is very inclusive and could be read as Fox (The Schocken Bible) has translated it: “retain anger.” Normally we think of bearing a grudge as holding on to anger for a very long time, but the text does not force that meaning. The Word of God is just to not maintain your anger, and thus agrees with Ephesians 4:26: do not let the sun go down on your anger.
“but you must love your neighbor as yourself.” Although this is not one of the Ten Commandments, it was well known to be the second greatest commandment in the Torah, the Law, and it is quoted a number of times in the New Testament (cp. Matt. 5:43; 19:19; 22:39; Mark 12:31; Luke 10:27; Rom. 13:9; Gal. 5:14; James 2:8).
“neighbor.” The Hebrew word is rea’, sometimes spelled reya (#07453 רֵעַ or רֵיַע pronounced ray’-ah). The HALOT Hebrew-English lexicon says of its meaning that it, “includes a wide range of related meanings which are more closely defined by their respective contexts. …the general sense may be summarized thus: רֵעַ, without expressing a particular legal relationship, means those persons with whom one is brought into contact and with whom one must live on account of the circumstances of life….” Thus, depending on the context, it can mean “neighbor” (and it is used that way in the non-technical sense of someone you should be friendly with), friend, companion, fellow, another person.
The Law has a lot to say about how we should treat our “neighbors.” In fact, it is the basis of Jesus’ parable of the Good Samaritan (Luke 10:25-37). For more on how to treat neighbors, see Exodus 20:16-17, 21:14, 18, 35; 22:7-11, 14, 26. The Jews had differing opinions on who was a “neighbor.” Jesus answered this question. See commentary on Luke 10:27.