We go through seasons in our faith. There are summers when our faith is strong and bright and warm and our affection for Christ and his people is robust. There are springs and falls when our faith is weathering the occasional storm but it is consistent and never drops too far out of view. And then there are winters. The blustery polar vortex of trials and sorrows descend upon the landscape of our souls and prevail for months at a time. Our faith hibernates so deeply that we wonder if it will ever surface again. What hope do we have when our faith is no more than a single ember on the hearth of a drafty house with a winter storm bearing down on us? It’s the same hope we have when our faith is bright and strong and warm—Jesus. Because our hope is not in our faith; it’s in Christ.
Joel Beeke communicates this well:
Too many Christians live in constant despondency because they cannot distinguish between the rock on which they stand and the faith by which they stand upon the rock. Faith is not our rock; Christ is our rock. We do not get faith by having faith in our faith or by looking to faith, but by looking to Christ. Looking to Christ is faith.
Nor is it perfect faith, great faith, fruitful faith, strong faith that justifies. If we start qualifying our faith, we destroy the gospel. Our faith may be weak, immature, timid, even indiscernible at times, but if it is real faith it is justifying faith (Matthew 6:30). Our degree of faith affects sanctification and assurance, but not justification. Faith’s value in justification does not lie in any degree in itself but in its uniting us to Christ and His glorious achievement.
As George Downame illustrates, "A small and weak hand, if it be able to reach up the meat to the mouth, as well performs its duty for the nourishment of the body as one of greater strength, because it is not the strength of the hand but the goodness of the meat which nourishes the body."
Far too often we are prone to look to the quality of our faith, the quality of our conviction of sin, the quality of our evangelical repentance, the quality of our love for the brethren for confirmation of our justification, forgetting that it is Christ alone who saves by gracious faith alone.
Beeke draws a necessary and comforting distinction, namely, that there is an infinite difference between the strength of our faith and the strength of the object of our faith, which is Christ. The illustration he borrows about the hand feeding the mouth with meat helps give great clarity to this spiritual truth. While our feeble faith feeds, it is Christ who nourishes and strengthens.
We will have seasons to our faith. It will ebb and flow. It will rise and fall. It will be strong and weak. It will crest and bottom out. In reality, I guess you could say that we are spiritual manic-depressives, and when we are not at either of the poles, we are vacillating somewhere in between. Here’s our hope—Jesus’ power and love and grace do not ebb and flow, rise and fall, or crest and bottom out. He is the same yesterday, today, and forever (Heb. 13:8). So let your faith grow and shrink—that’s perfectly fine. It’s not your faith that saves you, it’s the One in whom your faith lies. And He never wavers.
 Joel Beeke, “The Relation of Faith to Justification,” in Justification by Faith Alone, ed. Don Kistler (Morgan, PA: Soli Deo Gloria, 2003), 93-94.