Pence told the crowd Wednesday evening that the shooting at the First Baptist Church of Sutherland Springs was the worst mass shooting at a church in American history and called the gunman "deranged."
Abbott began the service by praying "for healing and for help." He also proclaimed Tuesday a statewide day of prayer.
Authorities say Devin Patrick Kelley killed 26 in the attack, including the unborn baby of one of the women slain.
Apple released a statement saying it has offered the FBI technical advice after learning the bureau was trying to access Kelley's cellphone. The company says the FBI has not requested its assistance.