Can anyone explain the meaning of lines said by Portia to Nerissa of Act 1 Scene 2 ?

Portia: If I do were as easy as to know what were good to do, chapels had been churches, and poor men's cottages prince's palaces. It is a good divine that follows his own instructions: I can easier teach twenty what were good to be done than be one of the twenty to follow mine own teaching. The brain may devise laws for the blood, but a hot temper leaps o'er a cold decree: such a hare is madness the youth, to skip o'er the meshes of good counsel the cripple. But this reasoning is not in the fashion to choose me a husband. O me, the word "choose"! I may neither choose whom I would nor refuse whom I dislike ; is the will of a living daughter curbed by the will of a dead father. It is not hard. Nerissa, that I cannot choose one, nor refuse none?