When someone came to ask if he could become a chela of that guru, he might or might not enrol him by some sign such as giving him a flower, or putting a mark on his forehead.
In Go Make Learners : A New Model for Discipleship in the Church, I argued that John the Baptist and then Jesus both used water as a sign for enrolling disciples (John 4:1). Jesus' first disciples had been enrolled by John's baptism to begin learning how to prepare for the coming of the Messiah. Jesus would then have rebaptised the first of the twelve to begin learning from him. After the ascension new disciples were baptised to begin learning from the Holy Spirit. The only definition of the word Christian is a disciple who is being taught by the Holy Spirit about the Lord Jesus (Acts 11:26, see 11:24).
And a big difference, which could only have been initiated or commanded by Jesus, was that women as well as men could be baptised. Socrates had no female disciples. And as far as I know, it was not the custom of Hindu gurus to enrol female chelas. The modern gurus in America do this.
Among the rabbis it was unthinkable that a woman could enrol to study the Torah, and if it ever happened it was viewed as exceptional. This question is one of the hottest in modern Judaism. The reason is that if someone can become a disciple, it is only a matter of time before he or she begins functioning as a rabbi.
The astonishing thing was that all the baptisms recorded in the NT are immediate. There was never a moment's delay to check out the knowledge or sincerity of the would be learners. The long periods of catachuminate and probation that began by the second and third century were the first example of the legalistic counterattack which has continued to this day. When Paul was planting churches all over the Mediterranean it seems anyone could be taken in by baptism without condition to be taught by the Spirit (see Acts 16:33). And it was assumed that when you began learning you knew very little, and had no power to change yourself.
It is a plain fact that most of Europe was evangelized by lining up a tribe and baptizing them, and the teaching of the Spirit hopefully followed. This is also true of every overseas missionary area that I know of where there has been large church growth. I think the idea of the ascended Son of God being our rabbi and teaching us by the Holy Spirit is unique among world religions.