The ability to “weep with them that weep” (Romans 12:15) and the desire to “bear one another's burdens, that they may be light,” and “to mourn with those that mourn; yea, and comfort those that stand in need of comfort”, (Mosiah 18:8-9) are the marks of a good Christian. But in the New Testament, Paul said that a good Christian should also “Rejoice with them that do rejoice,” (Romans 12:15).
Most of us are good at the mourning with those that mourn, but when we Live in Truth we also rejoice with those that rejoice. I heard someone the other day criticizing a woman in her ward for “bragging and being boastful” about something good that had happened to her. But as she related the incident it sounded to me like the woman was simply excited about what had happened and joyfully sharing the news. If the woman had shared bad news or expressed negative feelings the person would have been compassionate and caring, but because it was good news she was labeled as boasting. Even worse some of us rejoice at other people's failings and misfortune.
When we Live in Truth we live in reality and we accept the good news as well as the bad. Instead of getting jealous or envious or being critical we simply mourn with the person who mourns and rejoice with the person who is rejoicing. So what if it is bragging? Let God worry about that. You don’t need to. Don’t vex yourself about it. Simply enjoy the moment with the person. Rejoice! Be happy for them! Delight in their excitement!
The magical thing about this is that as we rejoice with others our own joy increases.