One of the most potent sources of doubt is introduced in the early chapters of Genesis. It is Satan himself who causes Eve to doubt God by questioning His Word: “Did God really say you must not eat any of the fruit in the garden?” (Gen 3:1). Satan even tries to get the long-suffering Job to curse God (Job 1:11). Satan is said to be seeking to devour Christians (1 Pet 5:8).
This statement must not be taken literally, but means that Satan wants to devour the Christian’s commitment to God and testimony before others. One way he does this, is by introducing doubt into their mind.
The world system is another source of doubt. Since it has its own set of values and objectives that are opposed to God, it has also its own worldly wisdom (1 Cor 2:6). This wisdom stands in direct opposition to the wisdom of God taught by the Holy Spirit (1 Cor 2:13). It is clearly revealed, for example, in the opposition of the evolutionary theory to the truth of the creation of man (1 Tim 6:29).
Probably the greatest source of doubt Christians face is simply their own spiritual immaturity. James traces doubting in prayer to double-mindedness and instability (Jas 1:6-8). Paul explains that when Christians doubt sound doctrine, it is because they are children in the faith and thus are easily deceived (Eph 4:14). Conquering this kind of doubt demands a growing, obedient relationship with God.