I am 21 year old don't have enough knowledge about Islamic things. But I am notice that the digit 7 has a special importance in Islam . like seven earth, seven sky, seven ocean, seven Continent, seven round during hajj and umra, seven destinations in Quran, seven days in week. A lot of others example in universe. Can people clear me the actual meaning of digit seven and the history of this digit with some other examples?
The qur'an actually mentions many numbers the necessity to use them can have different reasons: To show the oneness of God to refute polytheism, to make clear that the statement of one witness is not enough based on the offense or sin which was committed and require a fix number, to add details to a story, to clearly define how heritance must be distributed, more generally as a fixed part in a ruling etc. so basically there's no reason why one should think that there's a special number. Nevertheless there are people and scholars that put emphasize on some mystic or numerological "facts" and "Observations" in and around the qur'an (I've pointed at some in the end of my answer on Does the idea of praying 5 times a day come from the Qur'an?. But most of these observations are pseudoscientific and shouldn't be taken too seriously. Even if they may help some people to raise their Iman. Note that the same actually applies to the hadith in ahadith our Prophet () mentioned some numbers, but there's always a clear reason why they were mentioned. And I doubt that this gives any special significance to this numbers for Islam in the whole, but it could have a significance in a specific context.
Numbers mentioned in the Qur'an
Here some examples of verses that mention numbers (not a full list):
- One in (2:61), (2:213), (4:11) (6:19)… this number has the most importance as Allah is one and that's the main message of all the Prophets and Messengers ().
- Two in (4:11), (5:106),(6:143), (6:144), (16:51).
- Three in (4:3), (4:171), (5:89) and (18:22)
- Four in (2:234), (2:260), (4:15), (9:2), (24:6) and (24:13)
- Five in (18:22), (58:7)
- Six in (7:54), (10:3), (11:7), (25:59), (32:4), (50:38) and (57:4) which all describe the creation of the earths and heavens in six days.
- Seven (2:29), (2:196), (2:261), (12:43), (12:46), (12:47), (12:48), (15:44), (15:87), (65:12), (69:7), (78:12) … beside the story of Pharao and the creation of seven heavens also other stories and a reference on the qur'an itself include the number seven.
- Eight in (6:143), (28:27) (39:6) and (69:17)
- Nine in (17:101), (18:25) and (27:48)
- Ten in (2:196), (5:89), (6:160) and (11:13)
- Eleven in (12:4)
- Twelve in (2:60), (5:12), (7:160) and (9:36) … mainly covering the twelve months of a year and the twelve leaders of Bani Israel.
- Nineteen in (74:30).
- Twenty in (8:65).
- Thirty in (7:142) and (46:15)
- you may also find verses quoting the numbers forty, fifty, sixty, seventy, eighty, ninety, hundred, two hundred, three hundred, thousand, two thousand, three thousand and hundred thousand (Some of these are already covered in the examples above).
Commentary on your examples
like seven earth, seven sky,
This is actually quoted above and known in the qur'an. As none of us knows what Allah exactly means with this we must accept it and wait for a divine answer or explanation.
This is certainly false, but maybe during the middle ages people thought there were 7 seas or something. But also has no relevance to the teaching of Islam.
This is subjective: When I was a child I've been taught there are 5 continents, later people started separating the two America's and so on. There's no actual relevance to Islam in that.
seven round during hajj and umra
All acts of Hajj and 'Umra actually have relevance in the story of Hajar and her son who were left by at the location of the Ka'abah. We are mainly only following their foot steps when performing the Hajj or 'Umrah rituals.
seven destinations in Quran,
I don't actually know what you are referring to?
seven days in week.
I guess this has established due to Allah's teaching of working six days and resting the seventh.