The traditional interpretation of the Greek word mikros, translated "little," seems to be of small quantity. This certainly would be true if you connected it with the teaching of Jesus about the wide and narrow gates. While it still would be valid to consider the "little flock" to be a small group relative to the whole, I think mikros should be used here as a qualitative term rather than a quantitative one.
In Acts 8:10, Luke uses mikros in "to whom they all gave heed, from the least [mikros] to the greatest..."
Hebrews 8:11?"And they shall not teach every man his neighbor, and every man his brother, saying 'Know the Lord', for all shall know me, from the least [mikros] to the greatest."
Consider that although the "good news" Jesus proclaimed was directed to all people, it was especially appealing to the poor, the crippled, and to those who did demeaning and what were considered to be despicable things to survive?the rejects of society. These people not only struggled economically and physically, they also suffered from what we would call "low self-esteem." They knew they were outcasts with no hope of ever improving their station in life. Also, many would have felt themselves abandoned by God, maybe because of sins they or even their parents or grandparents committed. Even those who were better off in society often saw themselves distant from God when they compared themselves to the religious leaders. Although some would have been bitter, resentful, or jealous, many simply resigned themselves to their life situation with a humility befitting the humble position society had assigned them, even though they may have yearned for something better. For these people, the good news of the kingdom was that "You are acceptable to God, and your time of relief is coming."
In Matthew 18, when the disciples argue over who is the greatest, Jesus calls a child over and tells them that unless they become like children, they cannot enter the kingdom. He goes on to state that the humility of the child is the key quality. Later, in Matt. 19:14, he says that the kingdom of heaven belongs to those like the children (meaning the humble). To me, this is an important connection, for in Luke, he said the Father was pleased to give the kingdom to the little flock.
Finally, looking at Matt. 18:12-14, Jesus tells of the one sheep that runs off from the flock, and the owner goes looking for it and finds it. In v. 14, he ends the story with "Even so, it is not the will of your Father which is in heaven, than one of these little [mikros] ones should perish. In the parallel passage, Luke 15:3-7, he ends the story with "...likewise joy shall be in heaven over one sinner who repenteth, more than over ninety and nine just persons, which need no repentance."
So, it looks to me that mikros, in this context, refers to a state of humbleness, of denial of self-importance. For some, this was fairly easy because it was part of their daily lives. For others?the wealthy, the powerful, the privileged, those held in high regard by others, or those who simply were proud?they had to set that aside and become like the disadvantaged, at least in attitude. Many could not, however. The people who came to John the Baptist to publicly confess sins, repent, and be baptized for forgiveness were the ones whom Jesus could minister to. The proud, elitist religious leaders did not recognize and respond to the call of God. The requirement of humility?of recognizing one's fallen, sinful, inadequate state, and the need for God's mercy?as a condition for entry into the kingdom, appears throughout the Gospels and in the NT letters.
I propose that "littleness" is a quality common to all the flock. That way, there is no problem of a flock within a flock. Either one is in the flock (kingdom) or is not.