What does « Truth / Sincerity » mean in the Quran?

Say, [O Muhammad], "If the home of the Hereafter with Allah is for you alone and not the [other] people, then wish for death, if you should be truthful.

Say, "Whoever is an enemy to Gabriel - it is [none but] he who has brought the Qur'an down upon your heart, [O Muhammad], by permission of Allah, confirming that which was before it and as guidance and good tidings for the believers."

And when a messenger from Allah came to them confirming that which was with them, a party of those who had been given the Scripture threw the Scripture of Allah behind their backs as if they did not know [what it contained].

And they say, "None will enter Paradise except one who is a Jew or a Christian." That is [merely] their wishful thinking, Say, "Produce your proof, if you should be truthful."

Righteousness is not that you turn your faces toward the east or the west, but [true] righteousness is [in] one who believes in Allah, the Last Day, the angels, the Book, and the prophets and gives wealth, in spite of love for it, to relatives, orphans, the needy, the traveler, those who ask [for help], and for freeing slaves; [and who] establishes prayer and gives zakah; [those who] fulfill their promise when they promise; and [those who] are patient in poverty and hardship and during battle. Those are the ones who have been true, and it is those who are the righteous.

And complete the Hajj and 'umrah for Allah. But if you are prevented, then [offer] what can be obtained with ease of sacrificial animals. And do not shave your heads until the sacrificial animal has reached its place of slaughter. And whoever among you is ill or has an ailment of the head [making shaving necessary must offer] a ransom of fasting [three days] or charity or sacrifice. And when you are secure, then whoever performs 'umrah [during the Hajj months] followed by Hajj [offers] what can be obtained with ease of sacrificial animals. And whoever cannot find [or afford such an animal] - then a fast of three days during Hajj and of seven when you have returned [home]. Those are ten complete [days]. This is for those whose family is not in the area of al-Masjid al-Haram. And fear Allah and know that Allah is severe in penalty.

Kind speech and forgiveness are better than charity followed by injury. And Allah is Free of need and Forbearing.

O you who have believed, do not invalidate your charities with reminders or injury as does one who spends his wealth [only] to be seen by the people and does not believe in Allah and the Last Day. His example is like that of a [large] smooth stone upon which is dust and is hit by a downpour that leaves it bare. They are unable [to keep] anything of what they have earned. And Allah does not guide the disbelieving people.

If you disclose your charitable expenditures, they are good; but if you conceal them and give them to the poor, it is better for you, and He will remove from you some of your misdeeds [thereby]. And Allah, with what you do, is [fully] Acquainted.

Allah destroys interest and gives increase for charities. And Allah does not like every sinning disbeliever.

And if someone is in hardship, then [let there be] postponement until [a time of] ease. But if you give [from your right as] charity, then it is better for you, if you only knew.

He has sent down upon you, [O Muhammad], the Book in truth, confirming what was before it. And He revealed the Torah and the Gospel.

The patient, the true, the obedient, those who spend [in the way of Allah], and those who seek forgiveness before dawn.

So the angels called him while he was standing in prayer in the chamber, "Indeed, Allah gives you good tidings of John, confirming a word from Allah and [who will be] honorable, abstaining [from women], and a prophet from among the righteous."

And [I have come] confirming what was before me of the Torah and to make lawful for you some of what was forbidden to you. And I have come to you with a sign from your Lord, so fear Allah and obey me.

And [recall, O People of the Scripture], when Allah took the covenant of the prophets, [saying], "Whatever I give you of the Scripture and wisdom and then there comes to you a messenger confirming what is with you, you [must] believe in him and support him." [Allah] said, "Have you acknowledged and taken upon that My commitment?" They said, "We have acknowledged it." He said, "Then bear witness, and I am with you among the witnesses."

All food was lawful to the Children of Israel except what Israel had made unlawful to himself before the Torah was revealed. Say, [O Muhammad], "So bring the Torah and recite it, if you should be truthful."

Say, "Allah has told the truth. So follow the religion of Abraham, inclining toward truth; and he was not of the polytheists."

And Allah had certainly fulfilled His promise to you when you were killing the enemy by His permission until [the time] when you lost courage and fell to disputing about the order [given by the Prophet] and disobeyed after He had shown you that which you love. Among you are some who desire this world, and among you are some who desire the Hereafter. Then he turned you back from them [defeated] that He might test you. And He has already forgiven you, and Allah is the possessor of bounty for the believers.

Those who said about their brothers while sitting [at home], "If they had obeyed us, they would not have been killed." Say, "Then prevent death from yourselves, if you should be truthful."

[They are] those who said, "Indeed, Allah has taken our promise not to believe any messenger until he brings us an offering which fire [from heaven] will consume." Say, "There have already come to you messengers before me with clear proofs and [even] that of which you speak. So why did you kill them, if you should be truthful?"

And give the women [upon marriage] their [bridal] gifts graciously. But if they give up willingly to you anything of it, then take it in satisfaction and ease.

O you who were given the Scripture, believe in what We have sent down [to Muhammad], confirming that which is with you, before We obliterate faces and turn them toward their backs or curse them as We cursed the sabbath-breakers. And ever is the decree of Allah accomplished.

And whoever obeys Allah and the Messenger - those will be with the ones upon whom Allah has bestowed favor of the prophets, the steadfast affirmers of truth, the martyrs and the righteous. And excellent are those as companions.

Allah - there is no deity except Him. He will surely assemble you for [account on] the Day of Resurrection, about which there is no doubt. And who is more truthful than Allah in statement.