Hi Claire, regarding the topic of sins:
After the importance of sound belief in the One God, we have been given many methods whereby we gain rewards and expiate sins as well..
1.We have collective supplications for the repentance of all sins.
2. Performing prayers.
3.Performing ablution
4.Attending the Friday prayer
5.Waiting for prayer for example:
"Shall I not tell you of something by means of which Allaah erases sins and raises you in status?" (this is in regards to our level in the next life, In Islam paradise has many levels. Those who are best in conduct will be closer to Creator.)
They said: "Yes, O Messenger of Allaah."
He s.a.w.s. said: "Doing wudoo' (purifying our body before prayers) well even when it is difficult,( DR: e.g when it is too cold etc)
taking many steps to the mosques and waiting for prayer after prayer. That is (equivalent) to guarding the frontier."
(Sahih Muslim)
6.Doing good deeds.
7.Performing hajj or umrah the pilgrimage (erases all sins for the sincere) and lesser pilgrimage.
8. Fasting
9. Giving in charity
10.Asking for the forgiveness from those whom we have wronged (after ceasing the wrong)
11. Being kind to animals e.g
Narrated Abû Huraira radhiAllâhu `anhu: Allâh's Apostle sallAllâhu `alayhi wa sallam said, "A prostitute was forgiven by Allâh, because, passing by a panting dog near a well and seeing that the dog was about to die of thirst, she took off her shoe, and tying it with her head-cover she drew out some water for it. So, Allâh forgave her because of that." [Sahîh Al-Bukhari]
12. Removing obstacles from a path e.g:
Allah's Messenger
said,
"While a man was on the way, he found a thorny branch of a tree on the way and removed it. Allah thanked him for that deed and forgave him (his sins)."
(Bukhari)
13. Observing patience in a time of hardship.
14. Every good deed is charity. Verily, it is a good deed to meet your brother with a smiling face, and to pour what is left from your bucket into the vessel of your brother.
Source: Sunan At-Tirmidhi 1970, Grade:
Sahih
(please note, that people who accept Islam as a way of life as in convert have all their sins removed as well.)
There are more ways than this but I hope this gives you an idea. We get rewarded and we also expiate sins by living a life of righteousness.
Regarding inner peace:
Islam urges its adherents first to have proper faith and then to stay away or eschew wrongdoing/sinning either to self and others.
Sinning takes away from the tranquility of the heart.
An example would be soldiers who were a party to the oppression of others. Even when they have a free pass from the authorities their hearts will not find peace.Many who oppress others or who sin constantly lead lives of quiet desperation and as such resort to escaping from reality by the usage of intoxicants etc.
It is mind boggling how many performers with awful lifestyles or people who swindle others e.g financial field escape reality through the use of some kind of intoxicant.
We are helped by the Quranic world view, its admonitions and advice to that which is better. Quranic injunctions are not a hardship they lessen our burdens.
Here is an example:
They ask you about wine and gambling. Say, "In them is great sin and [yet, some] benefit for people. But their sin is greater than their benefit." And they ask you what they should spend. Say, "The excess [beyond needs]." Thus Allah makes clear to you the verses [of revelation] that you might give thought. (Quran 2:219)
Inner peace requires sound faith and staying away from ill deeds and living a righteous life whilst making amends when we fall short.
Here are a few verses of the Quran and sayings of the Prophet peace be upon him regarding these issues.
"Know ye (all), that the life of this world is but play and a pastime, adornment and mutual boasting and multiplying, (in rivalry) among yourselves, riches and children. Here is a similitude: how rain and the growth which it brings forth, delight (the hearts of) the tillers; soon it withers; thou wilt see it grow yellow: then it becomes dry and crumbles away. But in the Hereafter is a Chastisement severe (for the devotees of wrong). And Forgiveness from ALLAH and (his) good Pleasure (for the devotees of ALLAH). And what is the life of this world, but goods and chattels of deception."{57:20}.
"Stand firm (in the straight Path) as thou art commanded,
Thou and those who with thee turn (unto ALLAH);
And transgress not (from the Path): for He seeth well all that ye do.
And incline not to those who do wrong, or the Fire will touch you;
And ye have no protectors other than ALLAH, nor shall ye be helped."{11:112.113}.
"Those who do wrong but repent thereafter and (truly) believe,
Verily Thy Lord is thereafter Oft-Forgiving, Most Merciful."{7:153}.
"It was not ALLAH who wronged them, but they wronged their own souls."{30:9}.
"Those who oppress men with wrong-doing and insolently transgress beyond bounds through the land, defying right and justice:
For such there will be a Chastisement grievous."{42:42}.
"Go to Pharaoh, for verily, he is a transgressor. Say to him: Will you purify yourself?" 79:17-18
"Verily, among his people was Abraham, when he came to his Lord with a pure heart". 37:83-84
"He has succeeded who purifies himself, who remembers the name of his Lord and prays." 87:14-15
"Verily, the prayer prohibits immorality and wrongdoing, and the remembrance of Allah is greater." 29:45
"O ye who believe Let not some men among you laugh at others: it may be that the (latter) are better than the (former): nor let some women laugh at others: it may be that the (latter) are better than the (former): nor defame nor be sarcastic to each other, nor call each other by (offensive) nicknames: ill-seeming is a name connoting wickedness, (to be used of one) after he has believed: and those who do not desist are (indeed) doing wrong." {49:11 }.
"When the wrong-doers will be made to stand before their Lord, throwing back the word (of blame) on one another Those who were deemed weak will say to the arrogant ones: Had it not been for you, we should certainly have been believers The arrogant ones will say to those who had been deemed weak: Was it we who kept you back from Guidance after it reached you? Nay, rather, it was ye who transgressed. Those who had been deemed weak will say to the arrogant ones: Nay it was a plot (of yours) by day and by night: behold ye (constantly) ordered us to be ungrateful to ALLAH and to attribute equals to Him They are filled with remorse. When they see the Chastisement: We shall put yokes on the necks of the Unbelievers: it would only be a requital for their (ill) Deeds." { 34:31-33 }.
Those who believe and do good deeds are the best of creation. (Quran 98:7)
Verily, God does not wrong [anyone] by as much as an atom's weight; and if there be a good deed, He will multiply it, and will bestow out of His grace a mighty reward. (Quran 4:40)
And keep up prayer in the two parts of the day and in the first hours of the night; surely good deeds take away evil deeds this is a reminder to the mindful. (Quran 11:114)
Good and evil deeds are not equal. Repel evil with what is better; then you will see that one who was once your enemy has become your dearest friend. (Quran 41:34)
Anyone who performs good deeds, whether it be a man or woman, provided that he is a believer, shall enter Paradise. No one shall suffer the least injustice. (Quran 4:124)
Verily, Allah does not look at your appearance or wealth, but rather He looks at your hearts and actions.
Source: Sahih Muslim 2564, Grade:
Sahih (hadith)