What to do when doubts about faith arise?

هُوَ الْأَوَّلُ، وَالْاٰخِـرُ، وَالظَّـاهِـرُ، وَالْبَاطِـنُ، وَهُوَ بِكُلِّ شَيْءٍ عَلِـيْمٌ

He is the First and the Last, the Most High and the Most Near. And He is the Knower of all things.