One might say that the first statement of the Reformation was that a saint never stops repenting.
“So I find it to be a law that when I want to do right, evil lies close at hand. For I delight in the law of God, in my inner being, but I see in my members another law waging war against the law of my mind and making me captive to the law of sin that dwells in my members. Wretched man that I am! Who will deliver me from this body of death? Thanks be to God through Jesus Christ our Lord! So then, I myself serve the law of God with my mind, but with my flesh I serve the law of sin.” (Rom. 7:21-25)
Being a saint is about being a sinner who knows where to go with their sin.
A saint delights in the law of God; a sinner wars against it. A Christian does both. This is the struggle of the life of faith. Saint Paul goes so far as to say it is a law that, while he wants to do what is right, evil is right around the corner. By law, Paul means this struggle is an objective and immovable truth. And this evil is not the devil waiting to attack him, but rather the evil that still dwells within him. A saint is a sinner who has been forgiven and declared righteous for the sake of Christ alone. However, Paul does not believe there is a saint who is not simultaneously a sinner on this side of heaven. Every honest Christian knows this to be true. Every baptized member of the family of God knows exactly what Paul is talking about.
When a sinner is born again in baptism, a miracle happens. That person who was dead in trespasses and sin is now a new creation (1 Cor 5:17). Within that new creation is a new desire. A desire born of the Holy Spirit to love God and to love neighbor. But because the newly born Saint remains in this mortal flesh, sin remains as well. Therefore, good desires are not the only thing that is new. There is now a war within the person that was not there before. Paul describes this war as him against himself, the new creation fighting against the sin nature. Because this is the case, the saint can perform no perfectly good works: the desire is there, but they are always mixed with sin. Our good works are good, and yet unfortunately, they are also stained with self-righteousness, the desire to be acknowledged, or obligation (and therefore void of love). This reality leads Saint Paul to not only refer to himself as a sinner, but as a wretch. It might be uncomfortable, and certainly doesn't sound glorious, but a saint is a wretch who knows they are God's wretch. Being a saint isn't about not being a sinner. Being a saint is about being a sinner who knows where to go with their sin.
When Martin Luther nailed his 95 theses to the Castle Church door in Wittenberg, he began his argument with this: “When our Lord and Master Jesus Christ said “Repent,” he willed the entire life of believers to be one of repentance.” One might say that the first statement of the Reformation was that a saint never stops repenting. And if a saint never stops repenting, it must be the case that in this life, a saint never stops being a sinner. Like Paul, Luther understands that saints are sinners who know where to put their sin. They place it directly on Christ. The non-saint does not do this. The non-saint cannot live a life of repentance because repentance requires faith. Faith that sins are forgiven for the sake of Christ alone. The saint believes it is Jesus Christ and he alone that can deliver them from this body of death. A saint is a sinner, fully dependent on Christ.
The saint is a sinner for a little while, but they are a saint for all eternity.
Sometimes, when we talk this way about the Christian life, people hear something that isn’t being said. Something like “Christians are just wretched sinners, so why even try to be good or do any good?” This is not what is being said. The saint desires to do good and will act on that desire, and in doing so, his neighbor will be loved and served. That love and service will not be perfect. In fact, it will be riddled with sin. This fact does not detour the saint. They are God's wretch and have an appointment with repentance every Sunday morning. This is the life the saint is called to. A life of imperfect loving, serving, and living, leading to confession and absolution. This is the life of repentance.
So yes, a saint is a sinner. And while being a sinner may be the more outwardly obvious reality, it is not the more concrete one. The truth is the saint is a sinner for a little while, but they are a saint for all eternity. The war raging within the Christian has already been won by Christ. His cross says all sin belongs to him. His empty tomb says he has defeated every bit of it.