forgive me if this is too personal and dont feel you have to answer, what is it that you think that would make you sure you are one of the elect?
other people can answer that question if they want to
What makes me sure is the Holy Spirit testifies in my spirit that I am Gods.
I have love for my fellow believers and for the disciples and people of God, as well as for God.
I feel sad/sorrow for those who are lost. (Its a sorrow born in love for them, which for me is a foreign feeling but it's something that since ive been saved i have)
I am growing in my life as a Christian. While there are many areas of my life I can see I need improvement in, there are areas I can see have changed, where salvation changed me. A look at how far I've come shows me something positive.
All that said, there have been times I've struggled, struggled with doing what God asked of me, struggled with knowing if I belonged to Him during particularly difficult challenges, and during those times, and under those specific spiritual attacks, I remembered that God will let none of us go, that all of His people will never be anything but His and nothing can take us from His hand, and that I know I am His because I believed in truth on the Lord's life, death, and resurrection...(and as the Bible says: believe in your heart and confess with your tongue and you will be saved)
Sometimes you just hang on to that initial salvation moment and the Truth you know it is/was to remember that you belong to God during a spiritual attack. The enemy wants to take our assurance so sometimes you hang on to what you know..
That's likely what RC Sproul was talking about when he said you hang on to your love of Jesus.. that's likely what helped him during a particular spiritual attack, for me, I held onto my initial salvation and the fact I knew my belief was pure and true and therefore truly saved according to the Bible.
There is always going to be something the enemy can never take from you; know what it is and hang onto that during the darkest times. My suggestion is just to make sure it's a biblical standing because we answer Satan the same way Jesus did, using scripture.
Read Ephesians 6:11-12