Walter Marshall, The Gospel Mystery of Sanctification, Direction XI (pp.157,158)
You must therefore endeavour to continue and go on in the same right manner as I have taught you to begin this great work of believing in Christ, that your faith may be of the same nature from the beginning to the end, though it increase in degrees, for our faith is imperfect and joined with much unbelief in this world and we have need to pray still, ‘Lord, I believe; help my unbelief’ (Mark 9:24), and therefore we have need to strive for more faith, that we may receive Christ in greater perfection. If you find that your faith has produced good works, you should thereby increase your confidence in Christ, for salvation by His mere grace. But take heed of changing the nature of your faith, from trusting on the grace and merits of Christ, to trusting on your own works, according to the popish doctrine ‘that our first justification is by grace and faith only, but our second justification is only by works’.
Beware also of trusting on faith itself, as a work of righteousness, instead of trusting on Christ by faith. If you do not find that your believing in such a right manner as I have described does produce such fruits of holiness as you desire, you ought not to diminish, but rather to increase your confidence in Christ, knowing that the weakness of your faith hinders its fruitfulness. And the greater your confidence is concerning the love of God to you in Christ, the greater will be your love to God and to His service. If you fall into any gross sin, after the work is begun in you, as David and Peter did, think not that you must cast away your confidence and expect nothing but wrath from God and Christ, and that you must refuse to be comforted by the grace of Christ, at least for some time; for thus you would be the more weak, and prone to fall into other sins; but rather strive to believe more confidently that you have ‘an Advocate with the Father, Jesus Christ the righteous’, and that ‘He is the propitiation for our sins’ (1 John 2:1,2). And let not the guilt of sin stay at all upon your conscience, but wash it away with all speed in the fountain of Christ’s blood, which is opened for us, that it may be ready for our use on all such incident occasions; that so you may be humbled for your sins in a gospel way, and may hate your own sinfulness, and be sorry for it with godly sorrow, out of love to God. Peter might have been ruined for ever by denying Christ, as Judas was by betraying Him, if Peter’s faith had not been upheld by the prayer of Christ (Luke 22: 31,32).
If a cloud be cast over all your qualifications, so that you can see no grace at all in yourselves, yet still trust on Him that justifies the ungodly, and came to seek and to save them that are lost. If God seems to deal with you as an enemy, bringing on you some horrible affliction, as He did upon job, beware of condemning your faith and its fruits, as if they were not acceptable to God, but rather say, ‘Though He slay me, yet will I trust in Him; but I will maintain mine own ways before Him’ (Job 13:15). Strive to keep and to increase faith by faith, that is, by acting faith frequently, by trusting on God to keep and to increase it, ‘being confident, that He which has begun a good work in you, will perform it until the day of Jesus Christ’ (Phil. 1:6).