The word “if” is a conjunction that is “used to talk about the result or effect of something that may happen or be true” or “used to discuss the imaginary result or effect of something that did not happen or that is or was not true.” From these definitions, do you see how suspiciously the 
word “if” can be used? When used effectively, the word “if” can create all sorts of doubt, indecisiveness and mistrust in a heart where those things once did not exist.
Every time the devil tempted Jesus, the despot of disbelief threw that word at Jesus to try to kindle just one spark of doubt, indecisiveness or mistrust in the heart of Jesus. “If You are the Son of God…If You are the Son of God…” If he could get Jesus to question that truth for just a moment, that may have been all the foothold he needed to conceive sin in the Savior’s heart.
The despot of disbelief will throw that word at us, too. “If you really think there is a heaven…If you have never questioned God’s care…If you are so certain that everything in the Bible is true…” His hope is that he might get just one “if” to crack your faith. Is your shield ready?