Why is assurance something that believers seem to struggle with?
Because, ultimately, even for believers, it can be hard to believe the gospel.
A Shadow of a Doubt
I grew up in a Christian home, but to be completely transparent, I don’t know the date of my conversion. As I grew into my teenage years and even into adulthood, this presented a very big problem for me. I would hear well-meaning pastors and evangelists speak of salvation experiences that included a time and a place of conversion, but a time and place was not something that I knew. How could I be sure of salvation, “without a shadow of a doubt”, if I did not know the exact time and place?
In the case of myself and many others, this is a real problem that presents a great deal of anxiety. So how can we be assured of salvation?
The Source of an Undeceiving Assurance
Chapter 18 of the 1689 London Baptist Confession states that: “infallible assurance of faith is founded on the blood and righteousness of Christ revealed in the Gospel.”
The term ‘infallible’ that the framers of the confession use here comes from two Latin words which literally mean, ‘not deceiving’. It means not being able to be mistaken or deceived.
Author Sam Waldron explains that, this should reassure the one who says, ‘I want to have assurance, but I am so fearful of being mistaken and deceiving myself.’ There is an assurance of salvation that is available to all, which will not deceive you. 
So where do we find the source of this assurance that will not deceive us? The short answer is in the gospel!
I know that I am saved, know God, and am known by God, not because I have seen the Lamb’s Book of Life, because I know that my faith was sincere, or even because I believe that I repented sufficiently – I know that I am saved because I trust in Christ alone for my salvation. Hard stop!
Looking back over my own experiences, the root of my doubt was a misunderstanding of faith. When faith is seen as an action we do or an event that happens and doubt begins to creep up we are forced to pull out whatever checklist we may have at the time and begin evaluating our faith. But the scriptures are clear, the faith never belonged to us, to begin with.
Charles Spurgeon explains faith like this, “Faith occupies the position of a channel or conduit pipe. Grace is the fountain and the stream”. 
The apostle, Paul wrote, that our salvation comes “through faith” (Eph 2:8), and that “we have obtained access by faith into this grace in which we stand” (Rom 5:2)
Faith is the way that the grace of the gospel, flowing from Christ’s work, gets to us. This is why Paul describes the Christian life as one of continually ‘standing in grace’. So how do we get faith? The apostle clearly states that faith comes from hearing the gospel. (Rom 10:17)
If we understand faith correctly (as the channel through which grace flows from the work of Christ for us) then we will find that the “larger” our faith is – the greater our assurance can be.
Louis Berkhof explained this when he wrote that, “The more our faith grows, the greater will be our assurance”.
Many times the lack of assurance and the display of grace in our lives is due to our “channel” of faith becoming clogged by sin, trials, and just living in a fallen world. Peter tells us that it can even get to the point that the flow of grace becomes so weak that we forget that we ever experienced it to begin with. (2 Pet. 1:9)
So how do we increase our faith?
- Don’t trust yourself or your work for assurance.
Understand that it is not what you do, or don’t do, that brought salvation to you. Rather, remember that your salvation is found only through the work of Christ for you.
2. Turn to Christ and your unity with Him.
If you believe that Jesus died and rose again in your stead, then you have been reconciled to the Father, so turn you focus there. See that you have been reconciled by this work for you and know that you have been connected to Christ and are now and eternally in Him.
3. Connect yourself to a church and enjoy the means of grace.
Some have their assurance shaken, diminished, and intermitted because they neglect the means of grace by which we come to know our assurance. Connect yourself to an assembly of believers where you are constantly pointed to Jesus. We need to hear the gospel again and again because we are so apt to forget it. At times we need our faith pried open so that grace may flow again, and comes through hearing the word of God with a local assembly.
As believers, we can be most assured of our salvation when we are confident God has completely forgiven our sins through Christ’s death and resurrection. And we are most confident that God has forgiven our sins through Christ when we hear and are reminded of this good news.
In times of doubt, stop looking into and at yourself for assurance and look outward to the cross, look to the empty tomb, and look to the heavens where He ever lives for you.
 Reeves, Stan. The 1689 Baptist Confession of Faith in Modern English. (Cape Coral: Founders Press, 2021) 18.4
 Sam E. Waldron. A Modern Exposition Of The 1689 Baptist Confession Of Faith. (Darlington: Evangelical Press, 2013). pp. 279-280.
 Spurgeon, Charles, All of Grace (Chicago: Moody Publishers, 2010), 62-63.
 Berkhof, Louis. The Assurance of Faith (Port St. Lucie: Solid Ground Christian Books, 2004), 62