The Jaci Velasquez Christian song "Sanctuary" is about a Christian both glorifying Jesus and asking Jesus to help purify her mind and soul so that she can be a better "sanctuary" for Jesus. The speaker maintains gratitude throughout the song that she has this opportunity to become such a sanctuary for Jesus to reside in.
The first lyrics of the song establish both the singer's willingness to let Jesus in and the struggles that she has been through, as she is "tried and true." These lyrics also establish the frequent idea that her body is not a distant and dead place for Jesus to reside in, but instead is a "living sanctuary" that she regards with genuine "thanksgiving."
In the middle of the song, she both humbles herself and glorifies Jesus. She does so by recounting Jesus' mission to save the hearts and souls of individuals on earth, acknowledging that Jesus knows all of her weaknesses and still provides strength to her via their relationship.
Towards the end of the song, she calls more specifically on Jesus to utilize their relationship and to purify her. She asks to be taken away from temptation and to be purified "from within," leaving room in her cleansed heart for Jesus to inhabit and to "take away all my sin." The song finishes as it begins, with an invitation for Jesus to "prepare" her and use her as a sanctuary.