Sanctified means freed from both original sin and actual sin. It is what happens during baptism: we receive sanctifying grace.
Yes, it is also the end result of the process of sanctification. So it is both the start and completion. We must persevere in it to remain holy and be saved. (Most of us, though forgiven and possessing sanctifying grace, struggle with numerous venial sins and faults, and are liable to the penalties and consequences of our past sins.)
Being fully sanctified does not mean locked in a state of being unable to sin. That won’t happen until heaven.
No. He was conceived in original sin. But he was born without original sin. I also believe he remained sinless his entire life. Keep in mind he came in the spirit and power of Elias (Lk 1:17). Now Elias was taken up into heaven. If John the Baptist was greater than Elias, it is not hard to conclude that he remained sanctified.
Another who was born (not conceived) without sin is the prophet Jeremias:
Jeremias 1:4 And the word of the Lord came to me, saying: 5 Before I formed thee in the bowels of thy mother, I knew thee: and
before thou camest forth out of the womb, I sanctified thee, and made thee a prophet unto the nations. 6 And I said: Ah, ah, ah, Lord God: behold, I cannot speak, for I am a child.
If John the Baptist was greater than Jeremias, then it only follows that he was also sanctified, and not generically filled with the Holy Spirit (as might be said of King Saul).
Well, I have to look into the dogma aspect more deeply.
But suffice it to say that the Church has a feast day on his
nativity, and it is one of the oldest in the Church:
The commemoration of his Nativity is one of the oldest feasts, if not the oldest feast, introduced into both the Greek and Latin liturgies to honour a saint.
But why is the feast proper, as it were, of St. John on the day of his nativity, whereas with other saints it is the day of their death? Because it was meant that the birth of him who, unlike the rest, was “filled with the Holy Ghost even from his mother’s womb”, should be
signalized as a day of triumph.
newadvent.org/cathen/08486b.htm
Also, the Summa mentions this. It is certain that he was holy from the moment of his birth. And it is certain that he died a martyr.
hurst