One Nirguna (the Transcendent and the Unmanifest) Brahman (ब्रह्म / God) in Hinduism having many names to symbolize different potencies (शक्ति / बिभूति) as Ishwar (ईश्वर or Saguna Brahman) to help in worship and prayer

Consider the following hymns from the Rig Veda which show one Brahman (God) having many names:
"They call him Indra, Mitra, Varuna, Agni, and he is heavenly nobly-winged Garutman; To what is One, sages give many a title they call it Agni, Yama, Matarisvan." Rig Veda (Book 1, Hymn 164.46);
"He in his might surveyed the floods containing productive force and generating Worship; He is the God, and none beside him. What God shall we adore with our oblation?" Rig Veda (Book 10, Hymn 121.8 ).

While (Nirguna) Brahman is without attributes (formless, unmanifested and beyond comprehension) and cannot be worshiped directly, people use various names (reflecting various divine potencies / bibhutis) for Ishwar (Saguna Brahman as the Creator and Ruler of the World) --- including the names Agni, Indra, Savitar, Surya, Bhagavan, Brahma, Vishnu, Shiva, Ganesha, Devi, Bhagavati, Varuna, Vishvakarma et al. – to help in worship and prayer.

The personality (or symbol) used as deity during meditation and worship is mainly for spiritual significance and to reflect the real power (potency / bibhuti) of God (Ishwar). True bhakti (devotion) and the type (method) of worship depend on the nature, need, temperament, condition and situation of the devotee / worshiper.

A farmer, for example, may naturally be inclined to worship and pray to Ishwar using the name Varuna (implying the Lord of water), while he sees water as very important to him to get a good crop. A carpenter, repairer and builder of things, similarly, may be inclined to worship and pray to Ishwar using the name Vishwakarma (implying the architect and constructor of the World). Note, there is no difference, including in the benefits accrued, when the worship of Ishwar is performed by farmer using the name Varuna and by carpenter using the name Vishwakarma. There also is no difference in the outcomes (benefits etc.), additively / accumulatively, whether the worship involves the use of one divine name (Varuna, or Vishwakarma) or both names (Varuna as well as Vishwakarma).

As the worship of Brahman as Nirguna is not possible directly and physically, the believer in this case (Brahman as Nirguna in Creation and beyond basically) recognizes the entire Creation as a reflection of God and pursues spirituality accordingly (believing and acting to be one with Creation; the Bhagavad Gita: Ch. 12).

Regarding the worship / prayer of Brahman (God) as Ishwar or Saguna Brahman (as the Creator and Ruler of the World, and relevant in Creation), there are two types of worship: one is of a personal God as the Immanent, and the other by using symbols. In the case of the Immanent, worship usually occurs in the form of pure meditation and at the spiritual level.

Conversely, when the worshiper views God as external to him then the worship is symbolic (using symbols).

The symbols (objects and deities etc.) used in external worship are generally prakrit (comprising of Prakriti / Nature, which involve three modes or gunas -- sattva, rajas, and tamas). Note that the worshiper in this case should be mindful as to what the object of adoration (such as the deity / symbol in worship / prayer) and the method of worship (yajna, prayer etc.) stand for, because that will determine the outcome (fruit) of worship.

The object of meditation (worship) should be beyond or above the Law of Karma. It should not become a part of Sansara / World as a soul or the constituent matter and it should not be existing in the mode of darkness or ignorance (Tamas). Note that only Brahman (God / Ishwar) is above and beyond the Law of Karma, is changeless, and meets these conditions (the Bhagavad Gita: Ch. 5 - V. 29). On the other hand, when the meditation (worship) is intended to a secondary figure (such as a guru or a deity) who is subject to the Law of Karma, the results are secondary and of lesser value (the Bhagavad Gita: Ch. 9 - V. 25).

Ref.: Subhash C. Sharma, “Vedic vocations (Hindu castes) were not related to heredity (birth): (Note - 1: Brahman / God), ” (yr.) 2001, https://www.oocities.org/lamberdar/_caste.html