In Adventist theology, sanctification is a progressive process of being made more like Christ where one will have to get to a perfectly sinless state before the close of probation in order to stand before Almighty God without an intercessor. They teach that through the help of the Holy Spirit (the Helper), God will impart the righteousness of Christ (His divine merit) to you gradually over time making you more and more like Jesus (see the chart below). Obedience to the law, aided by faith in Christ, is the means by which one becomes sanctified. Eventually, you will get to a state where that impartation doesn’t have to happen anymore because you have developed a righteousness that mirrors that of Jesus’s. This is what they mean when they use the term “righteousness of Christ”.
Adventism teaches sinless perfectionism—that you can achieve sinlessness in your current human condition with the help of the Holy Spirit. This is actually what they think the good news is. Jesus paid the penalty for sin, living life as a man just like we are, but without sin, demonstrating that the Law of God is fair and can be kept. Christ, in their view, came to vindicate the Law as He was man’s Example.
This plays a larger role in their extra-biblical Great Controversy worldview.
While the Bible does teach that sanctification is a progressive progress, it isn’t a process of Jesus’s righteousness and character being gradually imparted to you by God, gradually over time, based on your obedience to the 10 Commandments. Rather, it is a work of God shaping and molding someone in the mortification of the “old man” that wars with the “new man” (Romans 6:6; Romans 7:14-25; 1 Thessalonians 5:23; 2 Thessalonians 2:13; 1 Corinthians 6:11). This war will take place the whole life of a Believer who will—eventually—be bodily resurrected and glorified (1 Corinthians 15:42–53) which will be perfect and free from sinful, fallen defects. Until then, the war will rage on as Believers keep warring with their sin. Perfection comes in the glorified state, not by having Jesus’s righteousness gradually imparted to you over time based on your behavior.
Believers will naturally have a desire to seek Christ and His desires for His people, this is because they have already been given the foreign, alien righteousness of Jesus entirely by faith (Philippians 3:9-10), not in small parts over time depending on your performance.