This is a great verse.  It gives the believer great hope of future glorification just like the promise of Romans 8:29-30 where Paul uses five verbs to describe how God sees the believer already in a glorified state.  Those five verbs are: He foreknew; He predestined, He called, He justified and He glorified.  So how do we look at the “if” of Colossians 1:23?  The false teachers at the time said God is important, but they added works to the spiritual growth process.  Paul is helping the Colossians see that faith alone in Christ alone is all that is necessary to be presented in glory, holy and blameless.  Let’s get the context:
²¹And you, who once were alienated and enemies in your mind by wicked works, yet now He has reconciled  ²² in the body of His flesh through death, to present you holy, and blameless, and above reproach in His sight–   ²³ if indeed you continue in the faith, grounded and steadfast, and are not moved away from the hope of the gospel which you heard, which was preached to every creature under heaven, of which I, Paul, became a minister.  (Col 1:21-23)

When Paul uses the “if” clause beginning in Colossians 1:23, it seems like the presentation is dependent on us.  “If we don’t continue, then we won’t be presented,” some might say.  But Paul states that the believer is already complete in Christ (Col. 2:10). So what must be done?

There are passages like Philippians 1:6 that confirm our completion when we see Jesus.  Paul prays that God will sanctify the Thessalonians completely at the coming of Jesus (1 Thes. 5:23-24).  Paul says, “He will do it!”  In Paul’s second letter to the Thessalonians, he prays that God would “fulfill all the good pleasure of His goodness and the work of faith with power” in the believer (2 Thes. 1:11).  Paul also writes to the Corinthians, “[Jesus Christ], who will also confirm you to the end, that you may be blameless in the day of our Lord Jesus Christ.” (1Co 1:8)   Peter prays, “But may the God of all grace, who called us to His eternal glory by Christ Jesus, after you have suffered a while, perfect, establish, strengthen, and settle you.” (1 Pet. 5:10)

So, in Colossians, was Paul making them doubt?  No, God sees them as glorified positionally.  But, they weren’t perfected yet.  They still were exhorted in Colossians 3, because they were failing over and over with many types of sins.  The first class condition is a statement of fact, or “if and the following clause is a fact.”  There are three other conditional clauses in the Greek that are for another study.

Paul did not doubt that they would continue and was positively affirming them (yet also exhorting them in Colossians 3).   Paul sees their growth as being fulfilled. They are like a building set on a firm foundation.  As the building is on a firm foundation, so they should stand upright to verify the firm foundation on which they stand – live a holy life, because they were bought with a price of the precious blood of Jesus Christ.  There was no earthquake (they were in a region of land movements) or storm that could shake them from their foundation on Jesus Christ.

So, Paul uses “if” as a First Class Condition clause (ei + indicative of the verb) whereby Paul assumes the Colossians will continue in their faith growth to demonstrate they have salvation.