Nonetheless, the Lord never distinguished between sins in terms of their ultimate penalty. 6 Jesus taught that every sin warrants eternal punishment in hell. He taught that the sin of anger brings the same punishment as the sin of murder (Matthew 5:21-22), and the sin of lust the same penalty as the sin of adultery (Matthew 5:27-30).
Perhaps this can help shed some light.
The justified person is not able for his whole life long to avoid all sins, even venial sins, without the special privilege of the grace of God. (De fide.)
The Council of Trent declared against the teaching of the Pelagians, according to which man, of his own natural powers, can avoid all sins his whole life long, that for this a special privilege of grace is necessary: Si quis hominem semel iustificatum dixerit … posse in tota vita peccata omnia, etiam venialia vitare, nisi ex speciali Dei privilegio, quemadmodum de beata Virgine tenet Ecclesia, A.S. (D 833); cf. D 107 et seq.; 804.
For the proper understanding of the dogma, the following must be observed: By “peccata venialia” are to be understood chiefly peccata semideliberata. “Omnia” is not to be conceived collectively, but distributively, that is, individual venial sins can be avoided with the help of ordinary grace, but not all venial sin, together. “Tota vita” means a long space of time. The “non posse” designates a moral impossibility. The “speciale privilegium” referred to embraces a total of actual graces, which form an exception to the usual order of grace, and indeed a very rare (speciale) exception.
According to Holy Writ, nobody is entirely free from all sin. James 3:2: “For in many things we all offend.” Our Lord teaches the just also to pray: “forgive us our trespasses” (Mt. 6:12). The Council of Carthage (418) rejected the Pelagian interpretation, according to which the saints ask for forgiveness, not for themselves but for others, or not according to the truth but only out of humility (humiliter, non veraciter) (D 107 et seq.; cf. 804).
St. Augustine makes this charge against the Pelagians: If all the saints could be assembled on earth and asked if they were without sin, they would, with one voice, answer with the Apostle St. John (1 John 1:8): “If we were to say that we were without sin, then we would deceive ourselves, and the truth would not be in us” (De nat. et grat. 36, 42).
The intrinsic reason lies in the weakness of man’s fallen will in face of his disordered motions, and in the wise ordinance of Divine providence, which permits lesser faults, in order to preserve the just man in humility and in the consciousness of his entire dependence on God. Cf. S. th. 1 II 109, 8.
Ott, L. (1957). Fundamentals of Catholic dogma (232–233). St. Louis: B. Herder Book Company.
Roman Catholicism, on the other hand, teaches that some sins are “light sins,” minor infractions of the moral laws of God [1862-1863]. Telling a small lie or stealing something inexpensive is somehow different from telling a big lie or committing grand theft. Small sins, venial sins, do not bring eternal punishment.
This seems like a contradiction of what he has said before:
“This is not to say that every sin is equally wicked or abhorrent to God. Scripture teaches that some sins are more evil than others and will be judged accordingly (John 19:11; Matthew 10:15).”
Additionally, the Roman Catholic Church teaches that, though venial sins may incline a person toward later committing a mortal sin, not even the regular practice of venial sins warrants eternal punishment. A baptized Catholic who does not commit a mortal sin remains in a state of grace even if he is habitually guilty of a multitude of venial sins. 
This is true
The Scriptures, on the other hand, teach that if a person’s life is characterized by sin, he should not consider himself a born-again Christian:
Little children, let no one deceive you; the one who practices righteousness is righteous, just as He is righteous; the one who practices sin is of the devil… No one who is born of God practices sin… 1 John 3:7-9
Again, there is no disagreement, I think their is a misunderstanding of Catholic teaching.
1863 Venial sin weakens charity; it manifests a disordered affection for created goods; it impedes the soul’s progress in the exercise of the virtues and the practice of the moral good; it merits temporal punishment. Deliberate and unrepented venial sin disposes us little by little to commit mortal sin. However venial sin does not set us in direct opposition to the will and friendship of God; it does not break the covenant with God. With God’s grace it is humanly reparable. "Venial sin does not deprive the sinner of sanctifying grace, friendship with God, charity, and consequently eternal happiness."134
While he is in the flesh, man cannot help but have at least some light sins. But do not despise these sins which we call “light”: if you take them for light when you weigh them, tremble when you count them. A number of light objects makes a great mass; a number of drops fills a river; a number of grains makes a heap. What then is our hope? Above all, confession.135
Catechism of the Catholic Church
By looking at this we can see that Venial Sins are commited mostly by a lack of understanding, or through ignorance, and because of this, it can lead to more harm such as mortal sin, unless we educate ourselves in the faith we are at serious risk.