>>> WHY was Jesus baptized ?
Well, first you need to understand what baptism signifies.
It signifies death of the body and resurrection into eternal life.
There was no need for Jesus to repent... but repentance is not baptism. repentance was a prerequisite for sinners TO baptism.
Jesus was baptized as the FIRST one to be resurrected... the ONE who would lead the way from death unto life.
I will re-read your post before I answer your first question.
Ah, maybe not. How about the practice of ritual cleansing preparatory to entering into one's ministry to satisfy the requirement of The Law? (Ex. 29:4, 40:12, other washings of the priest TNTC)
I believe this is what "unto all righteousness" means --