A thousand-bred horse is recognised by a person who can recognise excellent horse and make good use of it,so it is able to run for a very long distance (of thousands of Li).Mao Sui recommended himself and request for the cord,so he can make his way and show his talent,and thus become eminent.
意译的话,我猜是这样啦：
If a person wants to succeed,his talent needs to be recognised by someone.In order to do so,he needs to recommend himself to show his talent.