It would appear that the disciples were ignorant of the unbelief that had made them weak. They fancied that they had confidence in their Christ-given power, and they certainly had in some dull kind of fashion expected to succeed in their attempt. But He who sees the heart knew that there was no real living confidence in their souls; and His words are a solemn warning to us all, of how possible it is for us to have our faith all honeycombed by gnawing doubt while we suspect it not, like some piece of wood apparently sound, the whole substance of which has been eaten away by hidden worms. We may be going on with Christian work, and may even be looking for spiritual results. We may fancy ourselves faithful stewards of the gospel, and all the while there may be an utter absence of the one thing which makes our words more than so much wind whistling through an archway. The shorn Samson went out 'to shake himself as at other times,' and knew not that the Spirit of the Lord had departed from him. Who among us is not exposed to the assaults of that pestilence that walketh in darkness? and, alas! who among us can say that he has repelled the contagion? Subtly it creeps over us all, the stealthy intangible vapour, unfelt till it has quenched the lamp which alone lights the darkness of the mine, and clogged to suffocation the labouring lungs. I will not now speak of the general sources of danger to our faith, which are always in operation with a retarding force as constant as friction, as certain as the gravitation which pulls the pendulum to rest at its lowest point. But I may very briefly particularise two of the enemies of that faith, which have a special bearing on our missionary work, and may be illustrated from the narrative before us. First, all our activity in spreading the Gospel, whether by personal effort or by our gifts, like every form of outward action, tends to become mechanical, and to lose its connection with the motive which originated it. Of course it is also true, on the other side, that all outward action also tends to strengthen the motive from which it flows. But our Christian work will not do so, unless it be carefully watched, and pains be taken to keep it from slipping off its original foundation, and so altering its whole character. We may very easily become so occupied with the mere external occupation as to be quite unconscious that it has ceased to be faithful work, and has become routine, dull mechanism, or the result of confidence, not in Christ, whose power once flowed through us, but in ourselves the doers. So these disciples may have thought, 'We can cast out this devil, for we have done the like already,' and have forgotten that it was not they, but Christ in them, who had done it.