I heard a professing believer once say that he never doubts God nor his salvation in Christ. Being my usual inquisitive self, I probed further and asked, "Do you mean that you never doubt your faith?" He answered assuredly, "Never. I don't think a true Christian could doubt or else their faith is not real."
Well, I'll say it loud and clear because I know that the honest sinner out there will hear me: There are days when my faith seems unmovable and days when my doubting causes the spiritual ground under me to shake.
"For he saith to Moses, I will have mercy on whom I will have mercy, and I will have compassion on whom I will have compassion. So then it is not of him that willeth, nor of him that runneth, but of God that sheweth mercy." Rom 9:15-16
Dear saints, our salvation is not founded on our works, abilities, character or moral grounds. It is founded on the mercy of God on our poor, lost souls. We may have great strength of character and will of the mind (i.e. carnal faith) to be so assured of a truth whether it is of eternal things or of carnal things. Yet, that carnal faith does not save us unless God were to look mercifully on us and give us spiritual eyes to behold the Lord Jesus as our substitute for our sins and sovereign ruler of our souls. That is the difference between carnal and spirtual, God-given faith.
We are not saved because we have a perfect faith but rather that the One in whom we have faith is perfect and pure. Neither then does our faith exist merely in two states: Existent and perfect or not at all. For our faith grows He continues to reveal Himself to us.[Rom 12:3, 14:1] Nor was that faith granted only once to apply perfectly on the day that the Spirit revealed Christ to us. Instead, God continually grants us faith so that we might have the spiritual eyes necessary to look to Jesus who with one act perfectly accomplished all that was necessary to pay for our sins and please the Father. [Heb 12:2]
Christian, do not marvel at your weak seasons of faith nor be discouraged by them. Examine yourselves to see if you are of the faith. If you are a true believer, He will grant you mercy by causing you to look again to Christ. For as you continue to look to Jesus, He will - as the author and perfecter of faith - shine His face on you that you might see His majestic glory and merciful kindness. As a result, you will not extol the strength of your faith in pride but rather be humbled by His mercy once again toward you.