"For by one offering He hath perfected forever them that are sanctified".
We can see here three tenses; past, present and future. The N.I.V. verse says..."because by one sacrifice He has made perfect forever those who are being made holy". Sanctification, in experience, is a process...We may well fail, but we are not ' failures' !!! Christians need to bear in mind the 'tension' between the positional and the experiential aspects of their salvation. Positionally,they are forever sanctified, through the efficacious merits of Chris'ts Perfect Sacrifice at Calvary. Experientially, the aforementioned process is known.
[1] The Past...Christ's Perfect Atoning Sacrifice...2011 yrs.ago, (aprox.)...(Heb.9:10,11,14,28).
[2] The Present...Our Sanctification...The process by which we are fitted for Heaven...set apart from sinners, as was The Lord Jesus Himself...(Heb.7:26)
[3] The Future...Our Perfection...Our completeness in Him, Holy and without spot or blemish...(Eph.5:26-27).
May The Lord Bless you.