“Surely, while we teach that faith ought to be certain and assured, we cannot imagine any certainty that is not tinged with doubt, or any assurance that is not assailed by some anxiety.”- John Calvin
Doubt is common, and Calvin understood that we might experience it even after turning to Christ in faith. However, while we may not be able to touch and see the holes in Christ’s hands and feet, we can trust the Word of God and what it tells us about who Jesus is.
Source: http://www.christianitytoday.com/history/2009/august/justification-la-john-calvin.html