Why do you teach that women cannot be pastors?

Ephesians 4:11-12 states that a pastor is one of the five-fold ministry offices given to perfect the saints. The word translated "pastor" in this Scripture is the Greek word poimen, which means shepherd or supervisor. This word is one of only two ministry offices given by God that are grammatically masculine nouns with no feminine equivalent - the other word being Apostle. Each of the other offices are either neutral in gender and applicable to either sex (evangelist, teacher) or have specific masculine or feminine uses (prophet - male, prophetess - female). There is no such thing as a 'pastoress' or an 'apostless'. In other words - there are no female pastors or female apostles!.

The logic behind this distinction is clear when you examine the functions of these offices. Apostles are messengers sent by Christ to make disciples of the nations and to lay the foundation for local church congregations. The pastoral role is patterned after Jesus' role as our Chief Shepherd (1st Peter 5:4) and just like a shepherd, they are to feed, direct, heal, and protect the sheep (Jeremiah 3:15, Jeremiah 23:1-2). The performance of this role in seen in two ways - as shepherds and bishops (1st Peter 2:25). A shepherd guides and nurtures while a Bishop oversees the development of the flock. To fulfill the responsibilities of nurturing and overseeing the flock, a Pastor is equipped with a rod and a staff—a rod to discipline and correct and a staff to nurture and nudge in the right direction. The shepherd, bishop, pastor and overseer are all the same role.

The qualifications of a pastor are clearly delineated in 1st Timothy Chapter 3.
Specifically, 1st Timothy 3:2-4 states, "A bishop then must be blameless, the husband of one wife, vigilant, sober, of good behaviour, given to hospitality, apt to teach; Not given to wine, no striker, not greedy of filthy lucre; but patient, not a brawler, not covetous; One that ruleth well his own house, having his children in subjection with all gravity"

We see here that a man in this role must be the husband of one wife. This clearly disqualifies any woman from functioning in this role. We also see the reason for God making this distinction in verse 5, "For if a man know not how to rule his own house, how shall he take care of the church of God?"
A candidate for the pastoral office must first prove himself by demonstrating the ability to lead his household. Since we know that the man is the head of his family, this again eliminates the possibility of women serving as pastors (1st Corinthians 11:3, 1st Corinthians 11:7-9, Ephesians 5:33, 1st Timothy 2:12). Just as God has appointed man as the head of individual family units, God has also appointed man to lead the local church family of God.

The reason God makes these distinctions between the sexes is because the government of God is patriarchal. God is the Father of all spirits. Starting with the creation of Adam, God has continued to establish his authority in men. In evaluating the election of Abraham, we can see that God favored Abraham because he was a patriarch who had his house in order (Genesis 18:18-19). In fact, the last Scripture before the New Testament reads:

"Behold, I will send you Elijah the prophet before the coming of the great and dreadful day of the LORD: And he shall turn the heart of the fathers to the children, and the heart of the children to their fathers, lest I come and smite the earth with a curse." Malachi 4:5-6

God has not only established a patriarchal order of authority, clearly He expects us to respect that and operate in it.