Just imagine you are in a rather dingy shop and you like a sweater that you see on a model. It looks good but you as if you can take it to the doorway to see how it looks in the daylight. It looks quite different when you see it clearly.
Or again imagine you are going to bake a cake but the flour has some lumps in it. So you must sieve it until it is all white and smooth again. This is the real meaning of the word 'sincere' which Peter uses. It can be translated as 'pure'. It is not a common word in the Greek language which Peter spoke here but the Apostle Paul also liked this word.
What does this word mean for us as Christians? That is a really challenging question because it has to do with our mind, the thoughts we think, the words we speak, the very people we claim to be as followers of Jesus.
Think again of taking the sweater to the sunlight. Will your mind and thoughts stand the searching light of God and his Word?
Think again of the sieve sifting out the impurities. Will your mind stand that test or is it full of thoughts that shouldn't be there at all?
The sincerity the Bible speaks of is part and parcel of our Christian way of life. Peter said "I am stirring up your sincere mind by way of a reminder..."
Dear Lord, help me to remember to keep my mind clean and pure. Amen.