Just so you know, Spiritual maturity does not mean advancing in God's favor. It does not mean the work of salvation is incomplete. It most certainly does not mean that ‘you have arrived.’ It does not gain us access to Heaven, because this was done through the death and resurrection of Jesus Christ. It is through Jesus we are justified before God.
For all have sinned, and come short of the glory of God; Being justified freely by his grace through the redemption that is in Christ Jesus: Whom God hath set forth to be a propitiation through faith in his blood, to declare his righteousness for the remission of sins that are past, through the forbearance of God; Romans 3:23-25
It is through Jesus Christ that we are saved and have the promise of Heaven. Perfection does not come by maintaining a set of standards. It is possible for a person to maintain standards that give an outward spiritual appearance yet be unspiritual and maybe even unsaved; sweetly saved and cleaned up on the outside and filthy on the inside. Spiritual maturity does not depend on how you feel emotionally. It does not come automatically through years of being a Christian or by Christian service. Spiritual maturity [perfection] comes through an increase in and application of spiritual knowledge. This increase in knowledge comes by study of God's Word which results in understanding of the processes for perfection (spiritual maturity) and the commandments of our Lord Jesus Christ. Personal application of what we learn leads to spiritual maturity through the enabling power of God.
Apostle Paul calls the believers "saints" which means "sanctified ones.”
Unto the church of God which is at Corinth, to them that are sanctified in Christ Jesus, called to be saints, with all that in every place call upon the name of Jesus Christ our Lord, both their's and our's: I Corinthians 1:2
Yet in the same letter he corrects these "saints" because of sin.
Now I beseech you, brethren, by the name of our Lord Jesus Christ, that ye all speak the same thing, and that there be no divisions among you; but that ye be perfectly joined together in the same mind and in the same judgment. For it hath been declared unto me of you, my brethren, by them which are of the house of Chloe, that there are contentions among you. 1 Corinthians 1:10-11
They were believers and sanctified in Christ, but some of them were not living right in their daily conduct. These believers had received initial perfection. They were forgiven of their sins through redemption from dead works. These sins were forgiven once and for all
For by one offering he hath perfected for ever them that are sanctified. Hebrews 10:14
This initial perfection was received at the time they accepted Jesus as Savior. But these Christians had not gone on to perfection. They had not continued to put off the "old man" of sin:
Knowing this, that our old man is crucified with Him, that the body of sin might be destroyed, that henceforth we should not serve sin. Romans 6:6
Apostle Paul told them it was not right to continue living in sin after conversion. He said as a believer you should live a new life. It is not right to continue in sin.
What shall we say then? Shall we continue in sin, that grace may abound? God forbid. How shall we that are dead to sin, live any longer therein?
Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life. Romans 6:1-2, 4
We must go on to perfection [spiritual maturity]. Initial perfection from sin at the time of salvation is the start of a progressive life of sanctification. After salvation, you are to live a new life in Christ:
I am crucified with Christ: Nevertheless I live; yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by the faith of the son of God who loved me and gave Himself for me. Galatians 2:20
Apostle Paul described progressive perfection in his own life:
Not as though I had already attained, either were already perfect; but I follow after, if that I may apprehend that for which also I am apprehended of Christ Jesus. Philippians 3:12
Apostle Paul had not attained complete perfection [spiritual maturity], but it was his goal. He described his struggle for perfection in another passage:
For that which I do I allow not; for what I would, that do I not; but what I hate, that do I.
If then I do that which I would not, I consent unto the law that is good. Now then it is no more I that do it, but sin that dwelleth in me. For I know that in me [that is, in my flesh] dwelleth no good thing: for to will is present with me; but how to perform that which is good I find not. For the good that I would I do not: but the evil which I would not, that I do. Now if I do that I would not, it is no more I that do it, but sin that dwelleth in me. I find then a law, that, when I would do good, evil is present with me. For I delight in the law of God after the inward man: But I see another law in my members, warring against the law of my mind, and bringing me into captivity to the law of sin which is in my members. Romans 7:15-23
Apostle Paul desired to live by God's standards, but he realized that by himself [in his flesh; according to his self-nature] he could not achieve this goal. There was a constant battle between his flesh and his spirit. His spirit wanted to keep God's laws (vs 22). His flesh wanted to sin. He discovered that the only way he could achieve perfection [spiritual maturity] was through Christ:
And if Christ be in you, the body is dead because of sin; but the Spirit is life because of righteousness. But if the Spirit of Him that raised up Jesus from the dead dwell in you, He
that raised up Christ from the dead shall also quicken your mortal bodies by His spirit that dwelleth in you.
...but if ye through the Spirit do mortify the deeds of the body, ye shall live. Romans 8:10-11, 13
It is only through the Spirit of God that we can overcome the evil desires of the flesh and conform to God's standards. When the flesh results in us doing those things we would not, God has provided a way to restore us back to the path of perfection.
For if we confess our sins, He is faithful and just to forgive our sins and to cleanse us from all unrighteousness. I John 1:9
We do not have to try to live this new life in our own strength. We live it through "faith in the Son of God.” Whenever we fail, we can be restored to the path of perfection before God by confessing our sins and asking forgiveness. When we are born again, we are just like a baby in the natural world. There is much to learn spiritually. While we are learning we make mistakes. When mistakes are made, we must repent [regret] in our hearts, forsake [abandon] the unclean action, confess our sins and God will forgive us.
Now I rejoice, not that ye were made sorry, but that ye sorrowed to repentance: for ye were made sorry after a godly manner, that ye might receive damage by us in nothing. For godly sorrow worketh repentance to salvation not to be repented of: but the sorrow of the world worketh death. 2 Corinthians 7:9-10