did you mis-hear truth be told?
If so, it just means that the person saying it is being overly honest in saying something they might be unlikely or reluctant to say normally.
If not, I don't know!...
"Lo and behold" is an idiomatic, expression intended to convey emphasis and/or surprise: "I opened the door and, lo and behold, there was my long-lost husband."
This portion of scripture means Jesus wanted his mother to comprehend and gaze upon this picture of her natural son. And to never forget what she has seen this day, no matter what is said and or done...