13 Jesus answered and said to her, “Everyone who drinks of this water will thirst again; 14 but whoever drinks of the water that I will give him shall never thirst; but the water that I will give him will become in him a well of water springing up to eternal life.” John 4:13-14 (NASB)
Efficacious adj. producing the desired effect – from The Oxford New Desk Dictionary and Thesaurus Third Edition.
Christian faith has appeared to many an easy thing; nay, not a few even reckon it among the social virtues, as it were; and this they do because they have not made proof of it experimentally, and have never tasted of what efficacy it is. For it is not possible for any man to write well about it, or to understand well what is rightly written, who has not at some time tasted of its spirit, under the pressure of tribulation; while he who has tasted of it, even to a very small extent, can never write, speak, think, or hear about it sufficiently. For it is a living fountain, springing up into eternal life, as Christ calls it in John iv.1
Saving or efficacious faith is not the same thing as the best faith man can muster through the exercise of the will. According to our Lord Jesus in John 4:13-14 (above), efficacious faith is that which is given to the believer by God and this same faith will become in the believer a spring of water welling up to eternal life. This is not belief that is the product of reason or intellectual assent. It is not a belief that the believer must generate and desperately hold onto lest it be diminished and be lost. In the excerpt from Martin Luther’s letter to Pope Leo X, Concerning Christian Liberty, we read that those who conceive of faith as something done by the believer count it as simply a social virtue and that is an easy thing. Luther says that those with this concept of faith believe as they do because they have not experienced efficacious faith and have never tasted the great strength there is in it. I contend that the purveyors of the Seeker-Sensitive, Emergent, and Missional forms of “Christianity” are of the same sort of faith Luther is contrasting in this letter with genuine believers who are so because they have drunk of the water given to them by the Lord that has become in them a spring of water welling up to eternal life. These of the New Type of Christianity have a faith consisting of works-righteousness. This is a man-made faith not the efficacious faith that is a gift of God (Ephesians 2:1-10).