"'While I was with them in the world, I kept them in Your name. Those whom You gave Me I have kept; and none of them is lost except the son of perdition, that the Scripture might be fulfilled.'" (John 17:12)
So, Jesus did not lose anyone who our Heavenly Father gave to Jesus . . . except the one who was "the son of perdition". And I understand "the son of perdition" was Judas who apparently never obeyed Jesus, but was into getting money. So, I can see that if our Father gives someone to Jesus, Jesus does not fail to keep that person.
But even though our Father gave Peter to Jesus, Peter denied Jesus three times. But before Peter denied Jesus three times, here is what Jesus said to Peter > "'But I have prayed for you, that your faith should not fail; and when you have returned to Me, strengthen your brethren
.'" (Luke 22:32) So, Jesus knew that Peter would deny Him; so Jesus covered Peter in prayer, before Peter sinned against Jesus.
And this prayer was according to Jesus Christ's own faith; so Jesus' prayer was guaranteed to get better results than Peter could get by praying for himself according to his own faith
So, not only did Jesus' prayer get Peter back, but Christ's prayer made him also able to strengthen his brethren
, not only to get enough strength for himself. So . . . when we sin, Jesus Christ's intercession gets us back and also makes us able to love others as ourselves by ministering for others also to get stronger against sinning and get us more into living God's own love instead; "and you will find rest for your souls," (in Matthew 11:29) Jesus guarantees if we are walking with Him and learning how to personally submit to our Father and please Him (1 Peter 3:4) and care as much about others as our own selves.
So, if I am only worrying and arguing about what will or can happen just to me, I am not loving and caring about others as much as myself, not first busy with pleasing our Father; so this is not obeying how Jesus desires us to love. By the way, if you are the child of a human father whom you love so much, and you are in Daddy's lap and cherishing his warmth of affection, are you going to be thinking about how you can lose daddy
While Daddy's love is giving you such security, are you going to be asking, "Oh Daddy, what could I do that would have me lose you and stop being your child?"
"Are you going to be thinking of ways to get away from Daddy . . . to ice cream and candy . . . if you really love Daddy
"Now hope does not disappoint, because the love of God has been poured out in our hearts by the Holy Spirit who was given to us." (Romans 5:5) So, our assurance is our love life that we enjoy in submission and sharing with our Father; our assurance is not just some prayer we have said or Bible verse arguments. "Love has been perfected among us in this: that we may have boldness in the day of judgment; because as He is, so are we in this world." (1 John 4:17) So, our scriptural reason for "boldness in the day of judgment" is how You, O LORD our Father, are making us perfect in Your love which makes us as You are "in this world."
Also, Hebrews 12:4-11 shows that our Father is succeeding at correcting us, "that we may be partakers of His holiness." (in Hebrews 12:10) He is doing this now, "in this world." "But if you are without chastening, of which all have become partakers, then you are illegitimate and not sons." (Hebrews 12:8) So, our assurance includes how God is succeeding to correct us into how His love makes us holy, not to just stop doing certain wrong outward actions. So, by the way, it would not be enough, after we die, to be punished for certain sins, and be "purified", but now is the time to become loving with each other so we are prepared for how loving is for eternity.
And Your action, LORD, speaks louder than any words we can argue. So, this world does get people into a rut of arguing so our attention is away from where we belong.