An angel is a pure spirit created by God. The Old Testament theology included the belief in angels: the name applied to certain spiritual beings or intelligences of heavenly residence, employed by God as the ministers of His will.
The English word "angel" comes from the Greek angelos, which means 'messenger'. In the Old Testament, with two exceptions, the Hebrew word for "angel" is malak, also meaning 'messenger'. The prophet Malachi took his name from this word. He was himself a messenger, and he prophesied about the coming of "the messenger of the covenant", Jesus Christ (Malachi 3:1).
Although the word "angel" in the Bible, meaning a messenger, nearly always applies to heavenly beings, it can occasionally apply to human messengers. Malachi himself said a priest was a messenger (malak) of the LORD of hosts (Malachi 2:7), and in the Book of Revelation the elders of the seven churches of Asia were called angels (1:20; 2:1 etc.). But when we meet messengers doing supernatural things, there is no doubt they are heavenly beings - God's messengers, working for Him and for the ultimate benefit of mankind.
The Scriptures give us no indication of the precise time of the creation of angels; their existence is assumed at the earliest times. Our Lord often spoke of angels; in the New Testament they are numerous and seven orders are mentioned: Angels, Powers, Principalities, Dominions (ations), Thrones and Archangels the Old Testament specifically mentions two others Seraph (im) and Cherub(im). God bestowed upon angels great wisdom, freedom, and power, and their many appearances in the New Testament are indication of the lead role assigned to them. Both the New Testament and Old Testament refer also to the fallen angels. The Temptation of Adam and Eve presupposes the existence of bad spirits or demons who were cast into hell from which they have no hope of redemption. Angels are purely spiritual or bodiless persons (Mt 11:30), some of whom behold the face of God and thus are in bliss (Mt 18:10). These spiritual beings comprise the celestial court and are called angels (from the Greek for "messenger") because, according to the Bible, they carry out missions at God's command. In order to complete these missions, they can at times assume bodily form. According to the Bible, their missions are sometimes of great importance - eg, the Annunciation (Lk 1:26; 2:9-14). Like us , the angels are the objects of God's grace and love. But because, unlike us they are non-bodily creatures, their response to God's love did not require time and reflection to grow and mature. As soon as they were created and received grace, they had the opportunity to respond to God's love and thus be welcomed into bliss. While many did so, some did not. Perhaps the most significant continuing activity of the good angels is to be the agents of God's particular providence for mankind. Thus, the Church teaches that everyone has a guardian angel, based on references to them throughout the Bible.
The Creator Himself is so powerful and glorious that He cannot be approached in person by human beings. He alone "hath immortality, dwelling in the light which no man can approach unto: whom no man hath seen, nor can see (1 Timothy 6:16). Angels do not have man's shortcomings, and can therefore act for God and represent Him when communicating with men and women. They bridge the huge gap between the holiness and perfection of God in heaven and the shortcomings of dying people on this planet. Angels were made immortal (that is, never to die). Their eternal quality was spoken of by Jesus when he said:
"They which shall be accounted worthy to obtain that world, and the resurrection from the dead, neither marry, nor are given in marriage: neither can they die any more: for they are equal unto the angels; and are the children of God. being the children of the resurrection." (Luke 20:35.36)
Jesus was saying that, in the same way as the angels (the children or "sons" of God) live for ever and are of one gender, so those who will be called the "sons" and "daughters" of God when Jesus returns will also live for ever and will not marry.