These words are an expression of Lady Macbeth's thoughts during a soliloquy in Act l, scene V. She has just received word from her husband about his meeting with the witches, their predictions and that one of these - obtaining the title, thane of Cawdor - had actually come true.

She here expresses the wish that Macbeth should rush home so that she may lambaste him with brave and powerful words to encourage him to do that which he may be too afraid to do, which is to usurp the throne and claim it as his own.

The metaphor, 'pour my spirits in thine ear' suggests that she wishes to share her innermost thoughts and desires with her husband. She is keen to tell him about her passionate impulse for him to become king. 'The valour of my tongue' implies that she wishes to ply him with encouraging words which stem from her own courage to speak her mind. She wishes to spur him on into performing a most malicious and immoral act: obtaining the 'golden round,' which is the metaphoric description for the crown, by fighting and overcoming all the obstacles which may stand in his way.

Before saying the above, Lady Macbeth expressed uncertainty about her partner being ruthless enough to commit a heinous crime to get what he wants. She believes that he is 'too full of the milk of human kindness' i.e. that he is too soft and kindhearted to do anything rash or brutal to quickly and illegitimately obtain what he wants. The metaphor is apt since it alludes to a mother's softness and love when she is tenderly taking care of her baby.

In addition, she furthermore declares that her husband is ambitious but that he lacks 'the illness that should attend it.' This emphasizes the previous point. She is stating that Macbeth does not possess the insidious malevolence to act remorselessly in trying to achieve what he wants. In her contention, Macbeth deems certain things too sacred and with too much respect to commit evil.

It is, therefore, in her estimation, quite ironic that Macbeth should hold certain things (such as the crown and what it stands for) in such great regard and not try to obtain it by foul means but, paradoxically, still wish to win it (the crown) 'wrongly,' i.e. without following proper procedure.

For these reasons it is, therefore, imperative that Macbeth should haste home so that she may fervently speak to him.

Lady Macbeth speaks these lines after she has received Macbeth's letter.  In this letter, he acquaints her with the Weird Sisters' predictions that he would become Thane of Cawdor and king, as well as the fact that their first prediction has already come true. After she reads the letter, she speaks aloud her belief that Macbeth will be king; however, she also gives voice to her concern that he is "too full o' th' milk of human kindness / To catch the nearest way" (1.5.17-18).  In other words, she fears that Macbeth is too kind and compassionate, too loyal to Duncan, to be willing to kill him and take over the position of king that much more quickly. 

In the lines that you cite, Lady Macbeth says that she wants her husband to return home now so that she can influence him with her own ruthlessness and inspire him with the courage to take Duncan's position by murdering him.  She feels that she's capable of a great deal more brutality than he is -- a position in which she is, ultimately, incorrect -- and so she eagerly awaits his return so that she can compel him to behave as she would.