Matthew 18:20 AMP
[20] For where two or three are gathered in My name [meeting together as My followers], I am there among them.
In the chapter from where the verse above is taken from, Jesus lays down several primary principles and practices of His kingdom. Some of these include the power of prayer and the disciplne required to maintain it, the proper ranking in His kingdom, the joy heaven has when souls are saved from death and bought with precious blood into the saving knowledge of Jesus as Lord and Saviour. In all of the words in the whole chapter, it must be noted that Jesus was speaking to His disciples, and not the crowd. These words are for those who have made up their minds to follow and serve Jesus, and not for the many who are content to live 'convenient' lives.
The standards for the Christian are always higher and deeper than those for the unsure and uncommitted crowd. When you see a big crowd of people united in the pursuit of a thing or a purpose, do not always assume that they may be right. Being many does not always mean being right. Being many is not the same as being aligned with God's will and timing. The God who speaks here is a God of total and absolute knowledge; He cannot be deceived by platitudes, eye-service or sheer hypocrisy. The One who formed and made the heart sure knows its many dimensions and deceits. When I set my heart to do anything, I must always remember that God sees all.
I also believe that it was always part of God's plan that man work with other men to achieve anything. He has not made any human being absolutely self-sufficient. Even as God has commanded man, at creation, to be fruitful, to multply, and to fill and subdue the earth, man needs to work together with others to achieve these instructions. Recall the events of the tower of Babel, and you will realise the power that man has when he is aligned with others to pursue and achieve a goal. In this instance, the motive was wrong, and God had to disrupt the plans. Just imagine what could have been achieved if the motives were right, and the pursuit of God's glory was the focus.
That is what the verse above encourages and celebrates. With God, the number is not as important as the motive and the backup. If the glory and praise of God are the reasons why men are gathering, and not for the promotion of self, God is pleased to dwell amongst such people and to make Himself known. It does not have to be many; it just has to be focused on God. When the gathering is in His name, it means that He is glorified and exalted. Why would He not seek to show Himself strong and mighty amongst such people? Do not pursue numbers; pursue God's purpose. When He is there, mighty works follow. God's time of favour is here.