In the ancient Sanskrit/Pali language, the most basic meaning of "Buddha" is that of awakening or enlightenment. The word "Buddha" is also used to honor a person who has completely awakened to the true nature of existence. Often, Buddha also refers to Sakyamuni Buddha who attained the supreme enlightenment and started to teach us how to achieve the state of enlightenment about 2,500 years ago.
Therefore, the phrase "Be with Buddha" refers to the fact that we all have Buddha Nature. With Buddha Nature, each and every one of us will potentially become a Buddha. In other words, we are all future Buddhas. Being aware of such truth, we are already with Buddha. We seem so distant from Buddha only because our minds are filled with greed, anger, or ignorance.
In addition, "Be with Buddha" also means applying Buddhism in our daily lives. Buddha is compassionate, for example, thus we shall be compassionate. Buddha has no greed therefore we shall not be greedy. Buddha does not speak improperly or use improper languages to offend others, thus we shall not either. Instead, we should be ready to compliment, console, comfort and encourage others whenever and wherever appropriate. Buddha is of wisdom, thus we will be if we are with Buddha. Buddha practices all virtuous deeds and avoids committing any negative acts, thus we shall do the same. Buddha has a completely purified mind, therefore we shall maintain a pure and blissful mind.
If we all understand what "Be with Buddha" really means, we can all Be with Buddha.