Ephesians 1:3-13
3 Praise be to the God and Father of our Lord Jesus Christ, who has blessed us in the heavenly realms with every spiritual blessing in Christ. 4 For he chose us in him before the creation of the world to be holy and blameless in his sight. In love 5 he predestined us to be adopted as his sons through Jesus Christ, in accordance with his pleasure and will—

13 And you also were included in Christ when you heard the word of truth, the gospel of your salvation. Having believed, you were marked in him with a seal, the promised Holy Spirit…
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He chose us. When did that happen? Ephesians 1:4 – For he chose us in him before the creation of the world …

But we also had to choose Him. When did that happen? Ephesians 1:13 – And you also were included in Christ when you heard the message of truth, … When you believed …

It is not God unilaterally choosing me or me unilaterally choosing Him.  It requires both.

Think of a simple electrical circuit consisting of
1. an energy source (for example a battery)
2. a “hot” wire
3. a light bulb and
4. a neutral wire that completes the circuit.

The “hot” wire carries all the power but is not activated until the “neutral” wire is also connected. The neutral wire (our response to the gospel) has no power in itself. All the power is in the hot wire (God reaching out to us). But until the hot wire (God’s power) is connected to the neutral wire (our faith) the light bulb stays dark. Connect both and the light comes on.

God is the sole source of power. He reaches out to us with His powerful grace (the hot wire). When we respond in simple faith (the neutral wire) the circuit is completed and the light comes on (salvation and eternal life). It requires an action on our part but our action is simply a neutral response of faith which activates God’s power.
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Romans 11:22-23
Notice how God is both kind and severe. He is severe toward those who disobeyed, but kind to you if you continue to trust in his kindness. But if you stop trusting, you also will be cut off. And if the people of Israel turn from their unbelief, they will be grafted in again, for God has the power to graft them back into the tree.