Angels are created beings whose primary purpose is to be ministers of God's providence.  Whilst we can glean many of the properties of angels we lack much specific information. One of the few angels to be clearly delineated is Michael. He is mentioned 5 times and this paper will look at these references and attempt to ascertain the purpose and calling of Michael.
Angels were made higher than men but shall eventually be judged of men. They are spirits whose aim is to serve God by ministering to His own. They are greater than man in knowledge, strength and nobility although the fall short of God in each of these. Some angels have fallen; indeed Satan is a fallen angel of some order.
We are not told much about the hierarchy of angels although Rev 12:7 does imply that some order exists:
Re 12:7 And there was war in heaven: Michael and his angels fought against the dragon; and the dragon fought and his angels,
This tells us a number of things.
It is probable that this same event is referred to in Daniel 12:1:
And at that time shall Michael stand up, the great prince which standeth for the children of thy people: and there shall be a time of trouble, such as never was since there was a nation even to that same time: and at that time thy people shall be delivered, every one that shall be found written in the book.
The verse is clearly referring to a time of great distress and the mid-point of the tribulation (as in Rev 12) is a good candidate. Here Michael is specifically associated with the 'children of they people', which Daniel would have taken to be the Jews. This fits with the persecution of the Jews looked to in Rev 12&13.
The same theme of Michael being charged with the furtherance of the Jews is held in Daniel 10:21:
But I will shew thee that which is noted in the scripture of truth: and there is none that holdeth with me in these things, but Michael your prince.
Note that here he is your prince whereas when first introduced he is referred to as "one of the chief princes".
The other reference to Michael we have comes from Jude 1:9:
Yet Michael the archangel, when contending with the devil he disputed about the body of Moses, durst not bring against him a railing accusation, but said, The Lord rebuke thee.
Here again we see Michael defending the interests of the Jew. Again we see him locked into confrontation with Satan.
Here, uniquely, we see him referred to as 'the archangel'. The expression 'archangel' only appears in two places, once here and again in 1Th 4:16:
For the Lord himself shall descend from heaven with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first:
Some have suggested that this implies that Michael and the Lord are the same, although I doubt that. Michael means 'Who is like God'. I think his hall-mark is that he transfers the glory to God; he is not God himself.
One question that thus arises is "how many archangels are there?" In the KJV of Daniel 10:13 he is referred to as one of the chief princes. Again we do not really know, some of suggested Gabriel is one and tradition has suggested there may be seven. However the expression 'one of' could be rendered 'first of' and if there really are seven why didn't the Bible make it clearer? Further, if there are a collection of these then why was only Michael available to help Gabriel in Daniel 10 and why is only one used in the 'war in heaven'?
I think that if we tie these references together the picture we actually get is that Michael is probably the 'number 1' angel and their leader. He may have risen to that position after Satan fell. And whereas Satan fell by wanting God's glory Michael is noted for wanting to give the glory to God. Satan and Michael are in natural opposition (at least four and probably all five direct references refer to this). Michael's chief task during Jewish eras appears to be defending the Jew although he may be associated with the rapture too.
If my summary is correct then we get an interesting picture. Two of the highest order of beings: Satan and Michael. To anthropomorphize; they had similar abilities and a similar 'chance' in life and yet are in total opposition to each other. The only real distinctive is that one wanted glory for himself; the other wanted it for God. Perhaps as we go through life and work and achieve we need to ask ourselves: Is this being done for God's glory or our own?