2 Peter 1:10-11

10 Therefore, brethren, be all the more diligent to make certain about His calling and choosing you; for as long as you practice these things, you will never stumble; 11 for in this way the entrance into the eternal kingdom of our Lord and Savior Jesus Christ will be abundantly supplied to you.

Some would say that in order for the new believer to have assurance of his salvation, all he needs to do is to repeat over and over certain key verses like 1 John 5:11-12 and John 3:16. Well yes, that would be helpful. But that will gain you only a head knowledge of your salvation. The seven qualities (in verses 5-7) will do much more. By practicing them you will see your life change. You will see yourself bearing fruit for His kingdom. Hence, you will become aware that you have actually entered His kingdom; and that will give you the best assurance of salvation. For when a new believer (or even an old believer) sees that he is living the Christian life—that he is growing in moral excellence, in knowledge, in self-control, in perseverance, in godliness, in brotherly kindness, and in love—he will no longer stumble into doubt and fear regarding his salvation, but will instead have joy in the Lord for all that He does for him.