One of the reasons believers struggle with assurance of salvation is that they are looking in the wrong place.  A common error is that we take our eyes off our Saviour and we begin looking at our own faith or we look at our own life.  As we gaze upon SELF we get discouraged very quickly.

The believer looking within:

As I look at my own faith, I get discouraged. My faith seems to be shaky.  The more I look at my faith the more I begin to wonder and question:  "Do I really believe as I should?  Is my faith really good enough?  Am I really a true believer?  This is what usually happens as we get our eyes off the Lord and onto our own weak and frail faith.

Another similar problem is when I look upon my own Christian life.  I contemplate the way I have been living--my failures and faults and failings.  I begin thinking, "How can I be saved if I live this way?  I fall so far short of what I know God wants me to be.  Am I really His child?"

But God never told us to look at our faith for assurance of salvation.  He never told us to look at our own life and our own good works or lack of good works.  No, God tells us to be "looking unto Jesus, the Author and Finisher of our faith" (Hebrews 12:1-2).

The believer looking without:

What a difference it makes when I fix my eyes on the Saviour.  The more I look, the more I discover how wonderful my Saviour is and what a perfect salvation He has obtained for me.  "Faith cometh by hearing and hearing by the Word of God" (Rom. 10:17) because it is in the Word that I see my Saviour and learn of His sufficiency!  My faith is not wonderful, but my Saviour is wonderful and He is the One that I am trusting.  I am not trusting my faith, I am not trusting my good works, but I am trusting my Christ.  I'm not a person with great faith; I'm a person with little faith in a great God!  The more we get our eyes on the Lord--who He is, what He has done, what He has said--the more we will have that blessed assurance.

Faith is not some complicated thing.  Faith is simply looking to Christ (Isaiah 45:22; John 3:14-16).  Faith is seeing Christ as God pictures Him in the Word.  The question is not, "How good is my faith?"  The question is not, "How good is my walk?"  But rather the question is, "How good is my Saviour?"  The question is not, "Am I believing?" but rather it is, "IN WHOM am I believing and in what direction am I looking?"  Instead of desperately searching our deceitful hearts trying to find faith, we need to joyfully search God's Word looking to find Christ.

Spurgeon once said, "I looked at Christ.  The dove of peace flew in my heart.  I looked at the dove of peace. It flew away."  The same thing could be said about faith. Faith is fixing my eyes upon the wonderful Saviour of sinners!  When I turn my eyes away from Jesus and start gazing at my own faith or at my own quality of living, this is when I have problems.  I need to look away from SELF and see the Lord.

The Christian life is to continue in the same way that it commenced:   "As ye have therefore received Christ Jesus the Lord (by looking unto Him in simple childlike trust), so WALK YE IN HIM" (Col. 2:6).  Let's get our eyes on the lovely Saviour and move forward with our full confidence in Him!

See this link for a very helpful paper on Assurance of Salvation.