The whole question of faith and works has been hopelessly muddied by centuries of Protestant and Catholic polemic. Two points are worth keeping in mind, however.
First, in the main, the Reformers endorsed Abraham’s lament as spiritually legitimate. All the Reformation talk of forensic and imputed righteousness was meant to clarify the source of the possibility of good works, which comes from the grace of God alone. We do not give birth to the promise that creates an alternative to sin. The promise comes from God; it is imputed.
But the Reformers also agreed that we rightly expect God to make good on his promise of new life in Christ. On this point they were on common ground with their Catholic adversaries, who tended to think that the emphasis on grace alone had the effect of denying any actual human capacity for righteous deeds. In spite of polemical distortions that can lead us to think otherwise, according to both, if the promises of God are true, then faith must make a difference.
The second point is to remember that Genesis gives a great deal of space to the extraordinary delays and complications that emerge in God’s response to Abraham’s lament. Isaac is a long time coming, and the child disrupts Abraham’s household, bringing as much pain as joy. Thus, to return to the terms of James and the Reformation debates, we should not expect faith to produce good works immediately, and when faith does, we should not expect the righteous deeds of the true servants of Christ to be aglow with a pleasant, easy sanctity.