If thou canst answer me - The meaning of this verse is this: “The controversy between you and me, if you choose to reply, shall be conducted in the most equitable manner, and on the most equal terms. I will not attempt, as your three friends have done, to overwhelm you with reproaches; nor will I attempt to overawe you as God would do, so that you could not reply. I am a man like yourself, and desire that if anything can be said against what I have to advance, it should be offered with the utmost fairness and freedom.”
Stand up - That is, “maintain your position, unless you are convinced by my arguments. I wish to carry nothing by mere authority or power.”