The Rev. Dimmesdale keeps many vigils throughout the course of these seven years covered in The Scarlet Letter. We hear about them once, and then he heads to the scaffold in the middle of the night. I assume it's this event to which you're referring. Arthur feels the need to do more penance--more than fasting and keeping vigils and whipping himself bloody with a scourge.
He is tormented by guilt, and one night he goes to the scaffold. Many momentous things happen that night, as I'm sure you know--Arthur brings Hester and Pearl with him on the scaffold; Hester is struck by how weak and fragile he appears to be; Pearl asks him to stand with them in the daylight, and he refuses; Roger sees them but pretends he doesn't know the import of their being there together; a scarlet A is seen in the sky; a beloved governor dies.
In the morning, on a Sunday when everyone was gathering for church, Arthur's glove is found on the scaffold by a parishioner. The effect is as might be predicted--no one assumes the pastor they adore has been on the scaffold; instead they assume Satan is up to his old tricks, so to speak, trying to make a man of God look bad. Next time, says the parishioner with a laugh, the Reverend will just have to fight the devil with his bare hands.
If you're referring simply to the vigils--a prolonged period of prayer and watching, with no sleeping--they are making him weak. The weaker he gets, though, the closer the people think he is to heaven.
Either way. the effect on his career, then, is that he is even more revered by his "flock."
What I mean by that is it helps his career, not him.
I think the effect is ironic:while Dimmesdale is trying to punish himself, (his vigil being one of his ways), the vigil itself only makes him a better, more passionate speaker. Because of this, the townspeople adore and respect him even more, thus causing him even more pain.