First of all, "brother" is an intimate title, which means that the speaker has a younger brother.
Therefore, the sentence "My brother is the best copywriter" can be understood as: the speaker recognizes and appreciates his brother's advertising copywriter and thinks his copywriter is the best and most attractive. This may be based on my brother's actual experience and performance in the advertising industry, or it may be an emotional expression of the speaker to him.
In addition, this sentence can also be interpreted as an encouragement and support, that is, the speaker thinks that his brother can achieve greater success in this industry. This kind of encouragement and support can help my brother to be more confident and give full play to his talents in his work.
In short, the sentence "Brother is the best copywriter" is a kind of praise and recognition, which expresses the speaker's appreciation and love for his performance and talent in the advertising industry.