That's why we should remain a part of his body through a continued believing. For the passage also says if we deny him (which causes us to not be a part of his body) he no longer has any obligation to continue to remain faithful to us.
"If we deny Him, He also will deny us" - 2 Timothy 2:12
"if the unbelieving one leaves, let him leave " - 1 Corinthians 7:15
"If we deny Him, He also will deny us" - 2 Timothy 2:12
"if the unbelieving one leaves, let him leave " - 1 Corinthians 7:15