Michael Reeves shows how the Trinity is vital for Christian assurance of salvation in the sixth of nine short videos.
If God were different, I’m not sure we could have any assurance before him at all; because if God was simply the heavenly master bringing us before him, what confidence could we have before him? I’m not sure we could have any. If we’re simply his slaves then why would he not cast us off when we offend him? But with this God, it is very different. With this God, the Spirit unites us to his Son. And the sort of language you see Paul using, again and again, is that Christians are those who are “in Christ.” And therefore we are sons of God. Now, the Father could never, ever we can or cool in his love for his Son, let alone ever sent his Son away. And if we’re in the Son, he’ll never send us away, embraced by the eternal love of the Father. Christians are most safe in the Son, and with a father’s gift to the Son, he won’t let us away. And the Son makes us his gift to the Father. And he promises he’ll never let any be snatched out of his hand.