Is there a difference between sanctification and justification? Sure there is. Sanctified means "holy, purified, set apart" (to God) and Justified means "to declare one to be just, righteous" (with God's very own righteousness, not your own). Both of these are not something we do, but are conditions that we have received freely as gifts, by grace through faith.
While some people correctly believe that justification is instantaneous, they yet believe that sanctification is a process over time.
So what does the Bible actually say?
"By that will we have been sanctified through the offering of the
body of Jesus Christ once for all." Heb 10:10
"For by one offering He has perfected for all time those who are
sanctified." Heb 10:14
"I commend you to God and to the word of His grace, which is able to
build you up and give you an inheritance among all those who are
sanctified." Acts 20:32
"...that they may receive forgiveness of sins and an inheritance among
those who are sanctified by faith in Me." Acts 26:18
"To the church of God which is at Corinth, to those who are sanctified
in Christ Jesus..." 1 Cor 1:2
"But of Him you are in Christ Jesus, who became for us wisdom from God - and righteousness and sanctification and redemption..." 1 Cor 1:30
"But you were washed, but you were sanctified, but you were justified
in the name of the Lord Jesus and by the Spirit of our God." 1 Cor 6:11
Again, Sanctification means "made holy" and "set apart."
Our sanctification was just as instantaneous as our justification! It's not an
ongoing process. It already happened and it remains who we are at all times.
It's something we received as a gift when we first believed ("by grace, through faith"), not something based on what we do or don't do.