The Guardian Angels God given duties are: 

1) Guard against dangers to the body and soul.

2) Helps and guides  on the spiritual path.

3) Prompt to virtuous deeds and holy thoughts.

4) Admonish when sins are committed.

5) Intervene on behalf of humans.

Remember, Our Guardian Angels watch over us to offer protection, especially when our soul need protecting.  They aid our prayer by interceding for us, and help to prepare our souls for the moment when we stand before God at our death.