This is a follow up to this question:
This organization is the only official religious order in this setting. Although It has no official power within governments, it is widely revered as the voice of the main god and is deeply entrenched in civilized society. it operates as a priesthood, it also has many other functions. One branch operates as a police force, investigating crimes related to the supernatural. Another operates as a military order, defending the world from large outside invasions. Still another is an humanitarian organization, running shelters, hospitals, and the like or focuses on keeping the peace between countries.
This organization only accepts young children into its ranks. These are taken from their families at a young age normally after they are born, and raised by the org. itself to become members. This is a mandatory requirement for all nations. Then they are placed to whatever order needs their services. There are many capable adults and experienced professionals around the world who are willing to assist the org in its goals due to them being widely influential in all walks of life. However, it refuses their services and forbids new members over a specific age group. This tradition has been the rule since its inception.
Why would this order, at their own expense, only take in kids as new members?