"My child is yet a stranger in the world, she hath not seen the change of fourteen years" What language technique did Shakespeare use here?

Lord Capulet is speaking to Paris in reply to the young lord's request to marry Juliet in Act 1, scene 2. Shakespeare employs a metaphor, which is a figure of speech used to apply to a thing regarded as symbolic or representative of something else.

In this instance, Capulet is comparing Juliet's naivety, immaturity, inexperience, and youth to the lack of knowledge one has as a stranger to something. Juliet, he suggests, is much too young to consider marriage. She still has to learn...

Lord Capulet is speaking to Paris in reply to the young lord's request to marry Juliet in Act 1, scene 2. Shakespeare employs a metaphor, which is a figure of speech used to apply to a thing regarded as symbolic or representative of something else.

In this instance, Capulet is comparing Juliet's naivety, immaturity, inexperience, and youth to the lack of knowledge one has as a stranger to something. Juliet, he suggests, is much too young to consider marriage. She still has to learn about the world and gain the necessary knowledge to understand what it means to be wed. Furthermore, one can infer that Lord Capulet might be afraid that she, because of her youth, might embarrass the family and bring them into disrepute if she is married too young.  

Lord Capulet suggests that Paris should give her another two years and win her affections in the interim before he extends his suit again. He declares his love and affection for his daughter and states that "she is the hopeful lady of [his] earth," which means that his hopes are grounded in her to make him proud. He trusts that Juliet will not disappoint him. 

It is, therefore, ironic that Lord Capulet soon changes his mind and acquiesces to Paris' request in Act three, scene four.

Sir Paris, I will make a desperate tender
Of my child's love: I think she will be ruled
In all respects by me; nay, more, I doubt it not.

Furthermore, he is immensely upset when Juliet later rejects his instruction to get married. He rants and raves and calls her ungrateful. He also threatens to disown her and throw her into the street if she refuses.  

More irony lies in the fact that Juliet has already married Romeo at this juncture. In spite of her father's fear about her immaturity, she has taken it upon herself to get married. Her actions, therefore, shatter all hope that her father has had. She and her love's impulsive decisions create greater complications and eventually result in their tragic and untimely demise.