It depends upon what you ask your god to do, and how the DM wants your god to respond.
Beginning at 10th level, you can call on your deity to intervene on your behalf when your need is great.
You tell the DM you're going to use this feature (using your action if you are in combat), you roll percentile dice, and if you are successful, the DM decides what happens. As a guideline this could be an effect that's identical to any cleric or domain spell—not just a spell you could cast, but any spell—but there could be any other effect.
As a DM, I would weigh several factors in determining exactly what effect occurs, including:
- The domain(s), temperament, and nature of your deity. Talona and Bhaal are both deities of the Death domain, but they have distinct realms of influence and would respond to requests for aid differently.
- The nature of your request. Requests that are a poor match for your deity are more likely to have unpleasant side effects. Asking Bhaal (a god of murder) to return a dead character to life is more likely to be perverted (or to just fail) than asking Kelemvor (a god of the dead).
In general, the ability should be mostly positive for you if you succeed on your roll, especially if you're making a request that's consonant with your god's domains.
As an example, if your party was surrounded by enemies and unlikely to survive, and you called on your death-domain god to "save us", you might get:
- An antilife shell that surrounds you and your (nearby) companions for an hour, which might allow you to escape.
- A billowing cloud of black smoke that has the effects of the cloudkill spell without affecting you (and possibly your companions).
- You and your party are gated to your deity's plane.
- A powerful entity is gated from your deity's plane and sets to killing anything nearby, hopefully starting with your enemies.
- For the next minute, you and allies within 30' of you are surrounded by a frightful radiance that gives you advantage on all saving throws, and gives all enemies disadvantage on attacks against you, similar to the effects of the holy aura spell.
- Enough of your opponents are instantly killed for you to have a chance of surviving the fight.
- Three dozen zombies erupt from the earth around you, attacking everything nearby. They discorporate after a few minutes; hopefully you and your party were able to survive.
All of these are in line with the power level guidelines for the ability.
But note the important part about using Divine Intervention: You ask your god for something. You probably get nothing, and if you get something, the DM determines what it is. It should be generally favorable for you if your request was reasonable.