That single offering was Christ of course and it perfected for all time the salvation of the Elect.
who gave himself for us to redeem us from all lawlessness and to purify for himself a people for his own possession who are zealous for good works. (Titus 2:14 ESV)
He gave himself for us. He redeemed us. the "us" is believers, it is the elect just check Titus 1:1. That sacrifice was to purify for Him a particular people for his possession.. they are His and His alone!