If a person is persisting in minor sins, will praying for forgiveness be of any benefit so that they do not become major sins?
Question

                Can praying for forgiveness intercede in the case of minor sins which, if one persists in them, become major sins? Does persisting mean doing them whilst denying them or does denouncing them and also praying for forgiveness make them minor sins?
Praise be to Allah.The majority of earlier and later scholars of all groups are of the view that sins may be divided into minor and major. There is clear evidence to that effect from the Qur’an and Sunnah, as well as the statements of the earlier and later generations of the ummah. 
Sharh an-Nawawi ‘ala Muslim, 2/85 
We have explained earlier that it is not permissible to be careless about minor sins or regard them or what they may lead to as insignificant, because persisting in a minor sin is a major sin, and regarding them as insignificant and taking the matter lightly may lead to doom. 
Ibn al-Qayyim (may Allah have mercy on him) said: 
Persisting in a minor sin may be equal in seriousness to a major sin or even more serious. 
End quote from Ighaathat al-Lahfaan, 2/151 
See also the answers to questions no. 127480 and 130711
Secondly: 
Al-Qurtubi said: Persisting means resolving in the heart to do something and not give it up. Qataadah said: Persisting means adhering steadfastly to sin. 
Al-Mawsoo‘ah al-Fiqhiyyah, 36/305 
The one who persists in disobeying Allah and disobeying the Messenger is the one who is determined in his heart to repeat the sin whenever he has the opportunity; he is the one who is to be regarded as persisting in sin. 
Thirdly: 
The difference between repentance and praying for forgiveness: 
Shaykh Ibn Baaz (may Allah have mercy on him) was asked: What is the difference between repentance and praying for forgiveness? 
He replied: 
Repentance is regret for what has passed, giving it up, and resolving not to go back to it. This is called repentance. As for praying for forgiveness, it may be repentance or it may be mere words. A person may say: “O Allah, forgive me” or “I seek forgiveness from Allah,” but it is not repentance unless it is accompanied by regret and giving up the sin, and resolving not to go back to it. This is called repentance and it is called praying for forgiveness. The beneficial and productive kind of praying for forgiveness is that which is accompanied by regret, giving up the sin and resolving sincerely not to go back to it.
End quote from the Shaykh’s website 
http://www.binbaaz.org.sa/mat/10479 
What the individual must do is understand that true prayer for forgiveness means seeking forgiveness from Allah, may He be glorified and exalted. If he is not sincere in his request and does not seek forgiveness from Him, then it is just words that pass through his lips, without humbling himself before his Lord and without his heart focusing on his need for Allah, so what kind of prayer for forgiveness is this?! 
It says in al-Mawsoo‘ah al-Fiqhiyyah, 4/35: 
The kind of praying for forgiveness that is required is that which is accompanied by giving up the sin and resolving not to go back to it; it is not merely words that are uttered by the tongue whilst persisting in that sin. In that case it is (also) a sin for which he needs to seek forgiveness. End quote. 
An-Nawawi (may Allah have mercy on him) said: 
The scholars (may Allah have mercy on them) said: Persisting in a minor sin makes it a major sin. It was narrated from ‘Umar, Ibn ‘Abbaas and others (may Allah be pleased with them): There is no major sin if one prays for forgiveness and no minor sin if one persists in it. What is meant is that the major sin may be erased by praying for forgiveness, but the minor sin becomes a major sin if one persists in it. Shaykh Abu ‘Amr ibn as-Salaah (may Allah have mercy on him) said: The one who persists is the one who has the intention to do it again, which is contrary to the idea of repentance. Persisting in a minor sin could change it to a major sin.
End quote from Sharh Saheeh Muslim, 2/82 
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: 
Praying for forgiveness is of no benefit when one persists in sin, because it is closer to making a mockery (of faith) than to good deeds.
End quote from Thamaraat at-Tadween, p. 141 
Al-Bukhaari (6308) narrated from al-Haarith ibn Suwayd: ‘Abdullah ibn Mas‘ood told us two hadeeths, one from the Prophet (blessings and peace of Allah be upon him) and the other from himself. He said: “The believer sees his sins as if he is sitting under a mountain and fears that it may fall on him, and the evildoer sees his sins like flies that pass in front of his nose, and he does something like this to them [i.e., tries to swat them with his hand].” Then he said – and this is the marfoo‘ report – “Allah rejoices more over the repentance of His slave than a man who made a halt in a desolate place, and he has his mount with him on which is his food and drink, then he lies down and goes to sleep, then wakes up to find that his mount has disappeared, then when the heat and thirst or whatever Allah wills has become too much for him, he decides: I will go back to my place. So he goes back and sleeps for a while, then he lifts his head and sees his mount.” 
It is also narrated by Muslim (2744) but he did not mention the words of the mawqoof report. 
Al-Haafiz Ibn Hajar (may Allah have mercy on him) said in  Fath al-Baari, 11/105: 
The believer is overwhelmed by fear (of Allah) because of what he has of strong faith, so he does not feel safe from punishment because of that. This is how the Muslim should be, always fearing Allah and remembering that He is always watching, so he regards his righteous deeds as little and is worried about the smallest bad deed. 
Al-Muhibb at-Tabari said: Rather this is the description of the believer, because of his great fear of Allah and His punishment, for he is certain that he has committed sin but he is not certain of forgiveness. The evildoer has little knowledge of Allah, therefore he has little fear of Him and he regards sin as insignificant. 
Ibn Abi Jamrah said: What we learn from the hadeeth is that if a believer has little concern about sin and takes the matter lightly, this indicates that he is an evildoer. 
Ibn Battaal said: We learn from it that the believer should have a great fear of Allah, may He be exalted, with regard to every sin, whether it is minor or major, because Allah, may He be exalted, may punish for a minor sin, as He is not to be questioned about what He, may He be glorified and exalted, does. End quote. 
It is a sign of Ibn Mas‘ood’s understanding of Islam that he narrated this hadeeth after the other. The first one indicates that the believer should not take any sin lightly, whether it is minor or major, and that he should always fear its consequences in this world and the Hereafter. This is how the repentant believer is over whose repentance Allah rejoices greatly. 
With regard to the questioner saying “Does persisting mean doing them whilst denying them or does denouncing them and also praying for forgiveness make them minor sins?”, it is not very clear what is meant by that; we hope that what we have said in the answer is sufficient. 
And Allah knows best.