I've spoken with others who've, and I've done this myself, looked for assurance they are saved by focusing narrowly on their faith. The pitfall is this. As Christians we know we are saved by faith, so we zero in on faith. What we fail to see is the bigger picture. We are actually saved by grace (Eph. 2:8) and it is faith that introduces us to grace.
If you were looking for a job at your favorite company and had the opportunity to meet the owner who has the authority to give you the job you so desire, you would be excited! This opportunity could come in a variety of ways, perhaps an interview after you submitted a resume, perhaps someone you knew introduced you to the owner. Regardless, your hope would be that the owner would see you as a good fit and accept you for the position. So you shake hands, you answer the questions, and you leave the interview feeling good about it sure there are some parts you feel could have improved on but overall you feel good about the interview, even a bit confident that you'll get the job given your credentials.
But then... a couple weeks goes by and no phone call. The silence causes you to replay the interview in your mind, now questioning what you were once confident in. Answers you gave which you thought were solid you're now starting to wonder if they were actually well received. It's killing you. You want to know but how can you, what can you do. You don't have the boss's phone number so you can't call him, the friend who introduced you to him is away on vacation, the automated phone system only gives you the option to leave a voice mail.. so what do you do?
Because of the importance of this job, this once-in-a-lifetime opportunity you can't just sit idly by. This job is everything to you, you know it's the best opportunity you'll ever get and your life will be ruined if you don't make the cut. So full of anxiety you start replaying the interview in your mind over and over trying to glean something from it to convince you that the boss just hasn't made up his mind yet and that he still wants you... but the questions keep coming "what if he doesn't want me", "what if he found out about that thing I did in high school..", "what if I was only interviewed because of equal opportunity laws that require the boss to show that everyone has a fair chance even though they really don't". You just want to know and it's killing you!
If this analogy is starting to make sense, then I'm glad that salvation is important to you. Like the prospective employee in this analogy you've correctly deemed God's kingdom and offer of eternal life to be the best opportunity you'll ever have. However, this is where you (and I) error. When we think faith is an object to behold, we think we can find assurance by confirming we have it. The problem is, faith is not an object to behold but rather it's the Object of our faith that our eyes should be fixed on. When we focus in on faith we try to find assurance by replaying the interview, though no matter how many times we replay it it offers us none. What we really need is a call from the boss. Until then however, because of the value of salvation and the fear of coming up short, we frantically replay the interview in our minds, we call our friends and ask them to provide assurance that really they can't. After all it's not up to them if we get the job. It's not up to them if we are saved. What we really need is a call from the owner.
The interesting thing is, when we focus on faith to provide assurance what we're doing is trying to prove something in the flesh that cannot be seen with the flesh. Faith is spiritual and it's not tangible like a work. While one can look and see the accomplishment of his own works, faith is not a work and it in-and-of-itself accomplishes nothing. Rather it's Christ who accomplishes. Faith accomplishes nothing but rather it trusts in Christ to accomplish (Matt. 5:17). With your eyes on faith as to whether you have it or not would be like Peter trying to look at the waves and reason he can walk on them (Matt. 14:30). Peter could revisit this idea of walking on water many times and as long as he focused on the water he will never have assurance he can walk on it. However, with his eyes on Jesus he found confidence to step out of the boat when Jesus said "Come!" (Matt 14:29).
If you're looking at assurance for assurance then you may be in a similar conundrum. The answer isn't found there. Faith isn't anything and therefore it in-and-of-itself offers you nothing. It's the object of your faith that has value (Matt. 13:44, 46). What you need is a call from the Owner. Scripture instructs us this way,
2 fixing our eyes on Jesus, the author and perfecter of faith, who for the joy set before Him endured the cross, despising the shame, and has sat down at the right hand of the throne of God. - Hebrews 12:2
Romans 10:17 says faith comes by hearing (which I elaborate on in this series). So stop listening to your ability to listen and start listening to Christ!
32 Do not be afraid, little flock, for your Father has chosen gladly to give you the kingdom. - Luke 12:32
I believe the phrase "through faith" (Eph. 2:8) is one that should be amazing to us that grace comes so easily. Faith isn't always mentioned along side grace in the bible but I believe when it is it's not an equal partner but rather one that should profound us as to how easy it is to receive God's grace. Faith doesn't compete with grace for any splendor, that is due to God alone, but rather the mentioning of faith is a reference to how free grace is! Many will see grace and faith as both workers toward salvation but grace is where all the work is done, faith is merely the receptive avenue, it is the only way of receiving grace freely (Rom. 4:16). Faith shouldn't be looked at as something to behold nor should it gain any attention, but rather it should testify to the all sufficient grace of God. Faith is merely the assurance of grace. Faith should always point to grace, the moment faith garnishes any attention we've misunderstood it's role. Faith should make one marvel over the yoke of Christ, not as one who shares the burden of the yoke, but rather one who recognizes Christ bears the entire workload while we are attached to Him.
28 “Come to Me, all who are weary and heavy-laden, and I will give you rest. 29 Take My yoke upon you and learn from Me, for I am gentle and humble in heart, and you will find rest for your souls. 30 For My yoke is easy and My burden is light.” - Matthew 11:28-30