How do you make your calling sure? By faith alone? Or by faith and works?

What does it mean to make one's calling and election sure? Aren't those who are called and elected already saved?

And how do you make your calling and election sure, by faith alone? or by faith and works?

If they are already saved, why does Scripture say?
2 Peter 1:4-10

King James Version (KJV)
⁴Whereby are given unto us exceeding great and precious promises: that by these ye might be partakers of the divine nature, having escaped the corruption that is in the world through lust.
⁵And beside this, giving all diligence, add to your faith virtue; and to virtue knowledge;
⁶And to knowledge temperance; and to temperance patience; and to patience godliness;
⁷And to godliness brotherly kindness; and to brotherly kindness charity.
⁸For if these things be in you, and abound, they make you that ye shall neither be barren nor unfruitful in the knowledge of our Lord Jesus Christ.
⁹But he that lacketh these things is blind, and cannot see afar off, and hath forgotten that he was purged from his old sins.
¹⁰Wherefore the rather, brethren, give diligence to make your calling and election sure: for if ye do these things, ye shall never fall: