Hi Debra,

The word saint means sanctus or sacred and comes from the Latin meaning holy or set apart for God.

The Catechism tells us:

329 St. Augustine says: Angel is the name of their office, not of their nature. If you seek the name of their nature, it is spirit; if you seek the name of their office, it is angel: from what they are, spirit, from what they do, angel (St. Augustine, En. in Ps. 103,1,15: PL 37,1348) With their whole beings the angels are servants and messengers of God. Because they always behold the face of my Father who is in Heaven they are the mighty ones who do his word, hearkening to the voice of his word. (Matthew 18:10; Psalm 103:20)

330 As purely spiritual creatures angels have intelligence and will: they are personal and immortal creatures, surpassing in perfection all visible creatures, as the splendor of their glory bears witness. (cf. Pius XII, Humani generis: DS 3891; Luke 20:36; Daniel 10:9-12)

So in:

• Who they are, and
• What they do . . .
  

both men and angels have common similarities. For Christian men:

• The name of their nature is Christian, meaning they are men with a physical body and spiritual, eternal souls, which make up the Body of the Church.
• The name of what they do is preach the Gospel, if not by word, by the example of their life.

Angels will always be saints but not all mankind will be saints. Both Christian men and women are called to be saints by the public choices they make and witness of how they live their lives.

I hope this helps,

Mike