Mostly predestination. But with a text like the John 10 reading, can you really be surprised? The good shepherd knows the flock, even when dispersed, and the flock knows the voice of the good shepherd. You'll be dealing with predestination one way or the other.

John 10:22-30

“…but you do not believe, because you do not belong to my sheep. My sheep hear my voice. I know them, and they follow me. I give them eternal life, and they will never perish. No one will snatch them out of my hand. What my Father has given me is greater than all else, and no one can snatch it out of the Father’s hand. The Father and I are one.”
— John 10:26-30

Verse 27 by itself is quoted as the conclusion to Apology of the Augsburg Confession, Article 4: Justification (AP 4.173) as a bold statement that the institution of the church, running afoul of the gospel, even though it claims to be "the church" is not because those who live contrary to the gospel do not hear Jesus' voice.

Verses 26-29 are cited in an editorial insert in Formula of Concord, Epitome, Article 11: Election, Affirmative Thesis 4 (FC, Ep 11.5) to show the scriptural grounds for some kind of understanding of predestination.

Verses 27-30 are cited in Formula of Concord, Solid Declaration, Article 11: Election (FC, SD 11.12) as one of the scriptural passages about predestination that "strengthen our faith and assure us of our salvation" (FC, SD 11.12) rather than drive us to impenitence or despair.

Verses 27-28 are quoted a little later in the same article (FC, SD 11.30) as one of the ways scripture talks about those who are predestined for election.

Verses 28-29 are cited by editorial insert in Formula of Concord, Epitome, Article 11: Election, Affirmative Thesis 12 (FC, Ep 11.13) as part of a strong statement of faith regarding predestination. (Have a look, it's too long to type here but pretty solid!)

Verse 28 by itself comes up several times in Formula of Concord, Solid Declaration, Article 11: Election. (Yes, more about election.) First, this verse is quoted (FC, SD 11.8) as one explanation for God's foreknowledge of those who will be saved, that all of God's work is toward this salvation.

Verse 28 is cited again (FC, SD 11.46) in an interesting individualistic section that turns near the end to the communal reality of predestination. God cares deeply for each individual that will be saved, but has acted universally to ensure that Jesus might be the shepherd of those elected.

Finally, verse 28 is cited (FC, SD 11.90) in another statement of faith intended to comfort those troubled by the thought of having to attain and work to keep their own salvation. This is not the way God works! God has won salvation for us, and that salvation is kept by Jesus.

TheoThru

I recognize that most Lutherans preachers won't preach on predestination, preordination, and election, but given the John 10 reading and Psalm 23, the idea will be present whether you want it to be or not. We must pay attention to the assumptions others have about election and how those assumptions tend to run contrary to the gospel—moving people to ether impiety or despair. Jesus is the one who holds our salvation secure, and he was executed by a perversion of the justice system. We must be careful how we talk about what God knows and does as we talk about the good shepherd.

How have we paired a secular idea of success with eternal salvation?
Where does the gospel call us into action that might take us through the valley of the shadow of death?