Be true to yourself: when you say that “the task will be finished on time,” how much do you really expect this to happen? Aren’t you saying it with the hope that the task will be finished on time by itself? Aren’t you trying to take responsibility for the action off your shoulders and transfer it to the shoulders of the task itself?
Whether or not that’s what’s going on, trust me: that’s how it sounds to your readers, even if they don’t consciously realize it.
Every word has its personality, and some classes of words are stronger than others. Prepositions are timid links; articles are determined but sometimes intrude where they’ve not been called; adjectives are peacocks opening their tails whenever they have the chance.
And then there are the verbs. Verbs are the saw in the hand of the carpenter, the brush in the hand of the painter. It is through them that we transform the state of things. If it were not for the verbs, we would still be lying on the grass waiting for things to happen, without even being aware of what it means to be or to wait.
Maybe that’s why they cause fear: because using a verb is acting, and actions have consequences. Just as an inexperienced carpenter may be afraid of sawing the chair’s foot in the wrong place, thus destroying it, the inexperienced writer may be afraid of saying “This is so”; “John did such thing” ─ because with that she puts herself in the position of someone who knows how things are, and may be demanded for such knowledge.
And that’s the point where she turns to the active voice, like a carpenter who leans the saw against the chair, hoping they both will solve their issue by themselves.
The task will be finished on time.
I will finish the task on time.
If the second option doesn’t make you much more confident, then there’s something wrong with you.
That’s because the second sentence shows courage and confidence. The person who is saying it isn’t trying to hide behind the invisible hand of chance, which will make things happen (will it?), maybe with the help of an angel. The task will be finished… By someone… Maybe…
So whenever you have the chance, choose the active voice. By doing that, you will show to your readers that you are not afraid of what you’re saying. After all, if you’re not 100% certain of your words, it’s hard to expect that your readers will be.