_Satan’s second grand design against duties is to spoil them. (1.) _In the manner of undertaking, and how he effects this. (2.) In the act or performance, by distracting outwardly and inwardly. His various ways therein, by vitiating the duty itself. How he doth that. (3.) _After performance, the manner thereof._ The chief of Satan’s ways for the hindering and preventing of duty have been noted; what he comes short in this design he next labours to make up, by spoiling and depraving them: and this he doth endeavour three ways:— I. 1. First, By putting us upon services _in such a manner as shall render them unacceptable and displeasing unto God, and unprofitable to us_: as by a careless and rash undertaking of service. We are commanded to ‘take heed’ to ourselves ‘how we hear’ or pray; and to ‘watch’ over our hearts, that they be in a fit posture for meeting with God, because the heart in service is that which God most looks at, and our services are measured accordingly. If then by a heedless undertaking we adventure upon them, not keeping our ‘foot when we go into the house of God,’ Eccles. v. 1, we offer no other than ‘the sacrifice of fools,’ and give occasion to God to complain that we do but ‘draw near to him with our lips, while our hearts are far from him.’ 2. Secondly, The like spoil of duty is made when we adventure upon it _in our own strength, and not in the strength of Christ_. Satan sees the pride of our heart, and how much our gifts may contribute to it, and how prone we are to be confident of a right performance of what we have so often practised before; and therefore doth he more industriously catch at that advantage to make us forget that our ‘strength is in God,’ and that we cannot come to him acceptably but by his own power. Christians are often abused this way. When their strength is to seek, duty is oft perversely set before them, that they may act as Samson did when his locks were cut, who thought to ‘shake himself, and to go out as at other times,’ and so fell into the hands of the Philistines, [Judges xvi 20.] 3. Thirdly, If he can substitute _base ends and principles, as motives to duty, instead of these that God hath commanded_, he knows the service will become stinking and loathsome to God. Fasting, prayers, alms, preaching, or any other duty may be thus tainted, when they are performed upon no better grounds than ‘to be seen of men,’ or out of envy, or to satisfy humour, or when from custom, rather than conscience. How frequently did the prophets tax the Jews for this, that they fasted to themselves! and brought forth fruit to themselves! How severely did Christ condemn the Pharisees upon the same account! telling them that in hunting the applause of men, by these devotions, they had got all the reward they were like to have.