Are we sure assurance should be sought for?

[To S]

Luther's whole theology was driven by the question of how he could be assured of God's favour - how he could know that he was saved. He even defined faith as including assurance of salvation.

Our theology is shaped by the questions we asked. Was that the wrong question for Luther to be asking? Should we expect Christians to be sure of their salvation? Perhaps it is even unhelpful.

In contemporary Evangelicalism you could often assume that good emotions, and positive feelings are the primary purpose of all Christian activities. So we don't even think if there is anything wrong with Luther's question. But it is a question we should ask. Why is assurance of salvation essential to Christian faith?

Off the top of my head I would give two answers:

1. It honours God as truthful. To not be assured of your salvation is to call God a liar, because he promises just that in the Bible, the words of Christians, and the sacraments. "when the soul firmly trusts God's promises, it regards him as truthful and righteous. Nothing more excellent than this can be ascribed to God [this is the] very highest worship of God" (Martin Luther, The Freedom of the Christian).
2. It is the only way anyone will do good works. We will never be motivated to do truly good works by mere command, even less by fear. Unless we are sure that we have all that we need we will look first to shoring up our own salvation, before seeking to serve others. Unless we know for sure that God loves us we will not love him in return. A few quotes:

"For what reason is faith, as trust in God's promise [of our forgiveness], given priority over all works? In what way does it alone make all works good? Because it alone - and thus God alone, who establishes faith - breaks open the nature of the sinner as one curved in on himself; only he can loosen the fist that is clenched so tightly, so that my existence on behalf of others becomes natural once again and takes place with 'passion and love.' The imagery of receiving and passing on to others brings us to the foundational motif of Luther's understanding of God, that of categorical gift: through the Son, God in the Spirit gives himself to us as Father, in every sense of the word, so that we do not hoard and keep for ourselves what is given to us, which is what we do as sinners, but instead pass it on to others" (p. 283, Oswald Bayer, Martin Luther's Theology: A Contemporary Interpretation)

"if we recognize the great and precious things which are given us, as Paul says [Rom. 5:5], our hearts will be filled by the Holy Spirit with the love that makes us free, joyful, almighty workers and conquerors over all tribulations, servants of our neighbours, yet lords of all." (pp.304f, Martin Luther, The Freedom of the Christian)

"It is impossible to love God until the forgiveness of sins is first grasped by faith. For the heart that truly believes that God is angry is unable to love God until he is shown to be reconciled. For as long as he terrifies us and appears to be casting us into eternal death, human nature cannot bring itself to love such a wrathful, judging, and punishing God. It is easy for complacent minds to fabricate some foolish dreams about love [...] But in its agony and its battles the conscience experiences the emptiness of such philosophical speculations." (p. 126, Apology of the Augsburg Confession)