Adam Clarke on Hebrews 13:19

The rather to do this - That is, pray for us, that, being enabled to complete the work which God has given us here to do, we may be the sooner enabled to visit you. It is evident, from this, that the people to whom this epistle was written knew well who was the author of it; nor does there appear, in any place, any design in the writer to conceal his name, and how the epistle came to lack a name it is impossible to say. I have sometimes thought that a part of the beginning might have been lost, as it not only begins without a name, but begins very abruptly.