We know what kind of a person someone is primarily by what they do.
God created the world. He is powerful.
God has never tolerated sin. He actively wages war against it. He is holy.
God did not abandon us to evil. First he clothed us, then he sent his prophets and the law, and finally he gave us Jesus. He is faithful.
God poured out himself at great cost on our behalf. He is love.
Though we do not deserve salvation, he offers it to us and to those that believe the right to become sons of God. He is a merciful father.
He sent us his Spirit to intercede for us, to witness to Jesus, and to sustain us. He is with us.
He gives us wonderful gifts, not the least of which are the preaching of Gospel, the sacraments, and fellowship of the saints. He enjoys giving grace.
God’s personhood is absolutely vital in how we relate to him. It seems we get into trouble when we begin to relate to him a person he is not: the demanding taskmaster, the pushover dad, the distant diety, etc. We know, from his actions in history and in us, that he is a loving father full of mercy and grace, and that we may approach him as such.
Yet he is powerful and holy and will not be contained by finite creatures, and so we must also relate to him as what we are: small creatures desperately in need of redemption.