Wudu (ablution) is required in some situations; like prayer. As God would not accept a prayer without ablution. Other cases like tawaf (going around the Kabah) and holding Quran without cover also require wudu.
When ablution is required
Performing the ablution is required for the following:
1. Prayer.
:Ibn 'Umar quotes the Prophet (peace be upon him) as saying
‘Allah does not accept a prayer without ablution or voluntary charity (i.e. sadaqah) from stolen booty.’
2. Performing the tawaf (i.e. going around the Ka'bah), whether it be an obligatory duty or a voluntary act of worship. The Prophet (peace be upon him) is authentically reported to have performed ablution before doing the tawaf.
:He also said
‘Tawaf around the Ka'bah is a [form of] prayer, but Allah has permitted speech during it.’ Moreover, he made clear that women may not perform the tawaf when they are in the period.’
3. Holding the Qur’an without a cover.
:Allah says about the Qur’an
‘only the purified can touch it.’
(56:79)
:The Prophet (peace be upon him) said
‘None other than a person who has performed purification can touch the Qur’an.’
This is the view of many scholars, but the Qur’anic verse is preceded by a verse that mentions that the Qur’an is ‘in a well-guarded record’ which can be touched only by the angels, who are described as ‘the purified’. A large number of early eminent scholars are of the view that the Qur’an is permissible to be held by a person who has not performed the ordinary ablution, i.e. wudu’, provided that he has not incurred the need for grand ablution, i.e. ghusl.