"The Religion in the sight of Allah is Islam."
(Quran 3:19)

In another verse of the Holy Quran, Allah states:

"If anyone desires a religion other than Islam (Submission to Allah), Never will it be accepted of him; and in the Hereafter he will be in the ranks of those who have lost (their selves in the hell fire)."
(Quran 3:85)

In addition, Islam is the only religion prevailing over all other religions. Allah states in the Holy Quran:

"To thee We sent the Scripture in truth, confirming the scripture that came before it, and guarding it in safety:..."
(Quran 5:48)

Muhammad, the Prophet of Allah (Peace and blessing of Allah be upon him), said:
The superstructure of Islam is raised on five (pillars):

Testifying that there is no God (none truly to be worshiped) but Allah, and that Muhammad is the messenger of Allah, Performing the prayer (meaning the formal obligatory daily prayer of a Muslim, other non-formal prayers are not obligatory and may be performed when the person wishes),

paying the Zakaah (poor-due, an annual 2.5% {amount varies depending upon what is the nature of the wealth, e.g. gold, money, livestock etc} portion of your wealth which is to be distributed amongst the poor),

fasting the month of Ramadhaan (fasting from dawn to sunset),

Performing Hajj (a pilgrimage to the Kabah (sacred house built by Aadam and rebuilt by Ibraaheem) in Makkah, at least once in a lifetime for the person who is able to).

The Shahaadah can be declared as follows:

"ASH-HADU ANLA ILAAHA ILL-ALLAH WA ASH-HADU ANNA MUHAMMADAN RASOOL-ALLAH".

The English translation is:
"I bear witness that there is no deity (none truly to be worshipped) but, Allah, and I bear witness that Muhammad is the messenger of Allah",
However, it would not be sufficient for anyone to only utter this testimony orally either in private or in public; but rather, he should believe in it by heart with a firm conviction and unshakeable faith. If one is truly sincere and complies with the teachings of Islam in all his life, he will find himself a new born person.
This will move him to strive more and more to improve his character and draw nearer to perfection. The light of the living faith will fill his heart until he becomes the embodiment of that faith.
What would be next after declaring oneself a Muslim? One should then know the real concept underlying this testimony which means the Oneness of Allah and meet its requirements. One must behave accordingly, applying this true faith to every thing one speaks or does.
What do the words of the "Shahada" signify? The significant point which every Muslim must know very well is the truth that there is no God (deity) to be worshipped other than Allah. He - glory be to Him - is the only true God, Who alone deserves to be worshipped, since He is the Giver of life and Sustainer and Nourisher of mankind and all creation with His unlimited bounties. Man must worship Allah, Who alone is worthy of worship.
The second part of the Shahaadah (i.e., Wa ash-hadu anna Muhammadan rasool-Allah) means that Prophet Muhammad (sallallaahu ?alayhi was sallam) is the servant and chosen messenger of Allah. No one must have two opinions about this matter. In fact the Muslim has to obey the commands of the Prophet (sallallaahu ?alayhi was sallam), to believe him in what he has said, to practice his teachings, to avoid what he has forbidden, and to worship Allah alone according to the message revealed to him, for all the teachings of the Prophet were in fact revelations and inspirations conveyed to him by Allah.
What is the meaning of worship? It simply means rendering sincere service, showing reverence for Allah. In a deeper shade of meaning, it implies total submission and complete obedience to Allah's commandments both in utterances and actions of man whether explicit or implicit.
Worship fall into two categories:

Visible (manifest or outward)

Invisible (concealed or inward)

Visible worship includes acts such as uttering the two parts of the "Shahaadah", performing prayers, giving Zakaah (the poor-due), recitation of the Quran, supplication, adoring Allah by praising Him, purifying our bodies before prayers, etc.
This type of worship is associated with movement of the parts of the human body.
Invisible worship is to believe in Allah, in the Day of Judgment (in the Hereafter), in the Angels, in the Books of Allah, in the Prophets of Allah, in the Divine Decree of destiny (that good and bad are determined by Allah alone).
This type of worship does not involve movement of parts of the body but it surely has bearing on one's heart which subsequently affects one's way of life.
It should be borne in mind that any worship not dedicated to Allah alone will be rejected as one form of polytheism and this causes apostasy from the Islamic fold (for the one who believes that worshipping someone besides Allah is good and correct, the one who may have done this by mistake should immediately repent and seek Allah's forgiveness).
The next step for a new revert [1] to Islam is to purify himself by taking a complete bath. He should then resolve to comply with the principles and rules of Islam in their entirety. He should disown all forms of polytheism and false beliefs. He should reject evil and be righteous. Such rejection of evil and being righteous is one of the requisites of the motto of Islam - that is, Laa Ilaaha Illallaah. (none has the right to be worshipped except Allah)
Allah states in the Holy Quran:

"...whoever rejects evil and believes in Allah hath grasped the most trustworthy Hand-hold, that never breaks..."
(Quran 2:256).

We have to consider that when we declare from our heart that "there is no god (deity) worthy to be worshipped but Allah", it implies on our part love, devotion, faith and obedience to the rules of Islamic legislations which are legally binding on all Muslims. It is a requirement of "there is no god worthy to be worshipped but Allah" to love for the sake of Allah and to reject for the sake of Allah.
This is the firmest anchor of belief which materialise the meaning of "AL WALA" and "AL BARA". It means that a Muslim should love and be loyal to his Muslim brothers and sisters. He should, as a practice, dissociate himself completely from the unbelievers (those who stubbornly reject the faith of Islam) and refuse to be influenced by them, both in worldly and religious matters.
We conclude with a humble prayer to Allah that may He cleanse the hearts and souls of those who are genuine seekers of truth and may He bless the community of believers. Aameen.

Footnote: