Alleged sex offender Wytse De Vries would pray with the complainant when she went to bed, then return later in the night to indecently touch her.
"I betrayed my faith, and my God, my family - I'm ashamed," he told the Whanganui District Court on Friday as tears ran down his face.
De Vries is charged with two counts of sexual violation and four counts of indecent assault against two teenagers.
The 39-year-old pleaded guilty in 2014 to a representative charge of indecently touching one of the girls.
He has admitted through his lawyer, Fergus Steedman, that he offended against the victim "far more" than the girl remembers and than the offences he has been charged with.
Mr Steedman told the jury of five men and seven women that De Vries would plead guilty instantly to the charges if he believed they were accurately laid, but he took issue with the charges remaining.
"The defendant will deny emphatically that he ever touched [the second complainant]," Mr Steedman said.
De Vries also denies kissing the first complainant's breast and kissing her on the lips.
He took the witness stand on Friday morning, a number of times pausing to hang his head and breathing deeply. He appeared to fight back tears several times.
"There were periods of time when I withdrew myself from church fellowship and from communion, because I was over-ridden by guilt," he said.
He would regularly pray with the complainants before they went to sleep, but would later come back, kneel beside one of the complainants' beds, and "run my fingers through her hair or hold her hand".
"Later that led to me touching her breast."
He spoke of the first time he touched the complainant's crotch, claiming she pushed his hand towards it and raised her pelvis. The complainant denies this.
Crown prosecutor Harry Mallalieu questioned whether De Vries was "obsessed" with the complainant, which De Vries said he was not.
He could not explain the urge to go to her room and touch her, aside from that he was attracted to her developing breasts.
"Looking back it was not only risky, but shameful as well," he said.
Mr Mallalieu will continue his cross examination on Monday before Judge David Cameron.