How certain can one be in faith?

Very certain, but certainty comes in stages. It begins with drawing conclusions from signs and can grow into a personal experience of God's nearness.

Certainty in faith is not a switch that is either on or off. It has stages. A simple example makes this clear. If you see smoke rising in the distance, you conclude that there is a fire. That conclusion is reasonable, and nobody can call it false. If you come closer and see the flames, you are even more certain. And if you hold your hand near the fire and feel its heat, your certainty is strongest of all. None of these stages is a mistake, but certainty grows with each one.

Can one be mistaken? At the first stage, yes, it is possible. What looks like smoke may be dust in the light, and today there is even artificial smoke. A faith that rests only on reasoning, for example on reflecting about nature, therefore remains open to doubt. Yet it has one advantage. It can be explained and shared with others.

There is also the faith of simple people who grew up with it. It is often very firm, but it can hardly convince anyone else, because it has no reasoning behind it. Still, every person, learned or not, can move further. Whoever turns to Allah sincerely finds that prayers are answered and dreams come true. What began as a private experience becomes visible to others when what was foretold happens exactly as described.

The highest stage is the faith of the prophets. Allah speaks to them, and they live in His presence. Their faith does not rest on arguments alone but on a living relationship. The last verse above promises that Allah guides everyone who strives towards Him in His ways. So certainty is not something you simply have or lack. It is a path on which you can grow.