[Answer]-Filters and for loops in Django

Since you are looking for only 3 posts, there is no need to pull all of the entries, the following will be sufficient:

def all(request):
    """To get only three posts use a slice operation."""
    allPosts = Post.objects.all()[:3]
    context = {'Posts': allPosts}
    template = "home.html"
    return render(request, template, context)

You can find more in the official documentation:
https://docs.djangoproject.com/en/1.7/topics/db/queries/#limiting-querysets
If you need the results filtered, use the same concept, but apply your filters:
https://docs.djangoproject.com/en/1.7/topics/db/queries/#retrieving-specific-objects-with-filters

On the other hand if you are going to use all of them on the same post but just want to restrict only to 3 on a specific part (say a sidebar etc) from the same set, then you could fetch them all as in your original post, and then loops inside the template:

<div class="sidebar-module">
    <h4>Archive</h4>
    <ol class="list-unstyled">

    {% for singlePost in Posts|slice:":3" %}
        <li><a href="#">{{singlePost.title}}</a></li>
    {% endfor %}
    </ol>
</div>

Beware though that the above will result in a new query, if you are experiencing
load problems it would be better, to evaluate your queryset in the view, assign it to a list
and use the evaluated query:

def all(request):
    """The bellow evaluates the queryset before it hits the template.
    So slicing in the template (example before) will not result in a new
    Queryset."""
    allPosts = list(Post.objects.all())
    context = {'Posts': allPosts}
    template = "home.html"
    return render(request, template, context)

You can find more about evaluation here:
https://docs.djangoproject.com/en/1.7/ref/models/querysets/#when-querysets-are-evaluated