The purpose of a trading account is to ascertain the gross profit or loss of a business during a specific period of time. It includes all direct expenses such as the cost of goods sold and all direct revenues such as sales revenue. The trading account serves as an intermediary step towards calculating the net profit or loss of the business, as it only includes direct expenses and revenues, and excludes indirect expenses and revenues such as overheads and interest. By subtracting the cost of goods sold from the sales revenue, the trading account determines the gross profit or loss of the business.