It is sufficiently obvious in such a life as Abram's why faith is the one thing needful. Faith is required because it is only when a man believes God's promise and rests in His love that he can co-operate with God in severing himself from iniquitous prospects and in so living for spiritual ends as to enter the life and the blessedness God calls him to. The boy who does not believe his father, when he comes to him in the midst of his play and tells him he has something for him which will please him still better, suffers the penalty of unbelief by losing what his father would have given him. All missing of true enjoyment and blessedness results from unbelief in God's promise. Men do not walk in God's ways because they do not believe in God's ends. They do not believe that spiritual ends are as substantial and desirable as those that are physical.
Abram's faith is easily recognised, because not only had he not wrought for the blessing God promised him, but it was impossible for him even to see how it could be achieved. That which God promised was apparently quite beyond the reach of human power. It serves then as an admirable illustration of the essence of faith; and Paul uses it as such. It is not because faith is the root of all actual righteousness that Paul describes it as "imputed for righteousness." It is because faith at once gives a man possession of what no amount of working could ever achieve. God now offers in Christ righteousness, that is to say, justification, the forgiveness of sins and acceptance with God with all the fruits of this acceptance, the indwelling Divine Spirit and life everlasting. He offers this freely as he offered to Abram what Abram could never have won for himself. And all that we are asked to do is to accept it. This is all we are asked to do in order to our becoming the forgiven and accepted children of God. After becoming so, there of course remains an infinite amount of service to be rendered, of work to be done, of self-discipline to be undergone. But in answer to the awakened sinner's enquiry, "What must I do to be saved," Paul replies, "You are to _do_ nothing; nothing you can do can win God's favour, because that favour is already yours; nothing you can do can achieve the rectification of your present condition, but Christ has achieved it. Believe that God is with you and that Christ can deliver you and commit yourself cordially to the life you are called to, hopeful that what is promised will be fulfilled."
Abram's faith cordial as it was, yet was not independent of some sensible sign to maintain it. The sign given was twofold: the smoking furnace and a prediction of the sojourn of Abram's posterity in Egypt. The symbols were similar to those by which on other occasions the presence of God was represented. Fire, cleansing, consuming, and unapproachable, seemed to be the natural emblem of God's holiness. In the present instance it was especially suitable, because the manifestation was made after sundown and when no other could have been seen. The cutting up of the carcases and passing between the pieces was one of the customary forms of contract. It was one of the many devices men have fallen upon to make sure of one another's word. That God should condescend to adopt these modes of pledging Himself to men is significant testimony to His love; a love so resolved on accomplishing the good of men that it resents no slowness of faith and accommodates itself to unworthy suspicions. It makes itself as obvious and pledges itself with as strong guarantees to men as if it were the love of a mortal whose feelings might change and who had not clearly foreseen all consequences and issues.