There is power in agreement according to the Bible. What does this mean? It means if any two agree upon something, and the something is in accordance with the scriptures then God will see to it that it happens.
The Bible teaches that where any two/2 agree, it will be done by our Father which is in heaven. How can that be? It is all determined by what you are agreeing about.
For example, the Bible says 1 shall put 1000 to flight, but 2 shall put 10,000 to flight. This is regarding spiritual warfare. This formula also is in operation in other matters concerning spiritual things such as praying for someone to be healed, to praying for someone to become saved/converted to Christianity.
Where this becomes perverted and will not work is where the people praying in agreement do not understand the plan/works of God for a specific individual prayed for.
Some people will not be healed. Some people do not want salvation. Some people do not seek help in any of these things, so unless the people praying the prayer of agreement for whoever and for whatever reason, if it does not agree with God's plan for that specific individual it will never work, as free will must be respected for all beings.
This is the primary reason that not all are healed, saved, or whatever is asked for as the thing prayed for must be in agreement with God's will for the specific being in question.
God's word clearly says that not all will see, not all will understand, so when people are not healed or a miracle done for them, it is because it is not meant to happen when it is prayed for for that particular person at that time.
Timing is criticle for this prayer of agreement and the ones praying need to be "led by the Spirit of God within them"before it will happen or work at all.
In the book of Acts for example it is told there that the disciples and 120 other people came together in the first early gathering of the Church, when there were only about 120 believers but that they all believed the same thing, they were all in agreement in what they believed.
Then from Heaven came a rushing mighty sound, and cloven tongues of fire fell upon the people and the power of God fell upon all the people gathered and all the people of Jerusalem also saw and witnessed this event take place, and the population of the church was increased greatly that day, because the Bible says that they/the early Church were there all in agreement and so the power of God manifested because of their agreement in Spirit.
A miracle done in public because of the power of agreement.
So it is a good thing if all are in agreement, as long as they are in agreement with the word of God and these were it is stated.
There are also many other places in the Bible where when people were in agreement with something God said, that things always happened that blessed many people.
So when people are all thinking alike, things happen.