"If anyone would come after me, let him deny himself and take up his cross daily and follow me" (Luke 9:23). This is a painful process, and at times can discourage even mature Christians. The sins of self-intrest reach deep into the heart, and they are difficult to root out. Samuel Rutherford knew it well; likewise, he knew the only answer lay in the power of the One who said "follow me":
It is impossible that a man can take his lusts to heaven with him; such wares as these will not be welcome there. Oh, how loath are we to forego our packs and burdens, that hinder us to run our race with patience! It is no small work to displease and anger nature, that we may please God. Oh, if it he hard to win one foot or half an inch out of our own will, out of our own wit, out of our own ease and worldly lusts; and so to deny ourself, and to say, "It is not I but Christ, not I but grace, not I but God's glory, not I but God's love constraining me, not I but the Lord's word, not I but Christ's commanding power as king in me." Oh, what pains, and what a death is it to nature, to turn me, myself, my lust, my ease, my credit, over into my Lord, my Saviour, my King, and my God, my Lord's will, my Lord's grace!
But, alas! that idol, that whorish creature, myself, is the master-idol we all bow to. What made Eve miscarry? and what hurried her headlong upon the forbidden fruit, but that wretched thing herself? What drew that brother-murderer to kill Abel? that wild himself. What drove the old world on to corrupt their ways! who, but themselves, and their own pleasure? What was the cause of Solomon's falling into idolatry and multiplying of strange wives? what, but himself, whom he would rather pleasure than God? What was the hook that took David and snared him first in adultery, but his self-lust; and then in murder, but his self-credit and self-honour? What led Peter on to deny his Lord? was it not a piece of himself, and self-love to a whole skin? What made Judas sell his Master for thirty pieces of money, but a piece of self-love, idolizing of avaricious self? What made Demas to go off the way of the Gospel, to embrace this present world? even self-love and love of gain for himself. Every man blameth the devil for his sins; but the great devil, the house-devil of every man, the house-devil that eateth and lieth in every man's bosom, is that idol that killeth all: Himself.
Oh, blessed are they, who can deny themselves, and put Christ in the room of themselves! Oh, would to the Lord, that I had not a myself, but Christ; nor a my lust, but Christ; nor a my ease, but Christ; nor a my honour, but Christ! Oh, sweet word! "I live no more, but Christ liveth in me!" (Gal. 2:20). Oh, if every one would put away himself, his own self, his own ease, his own pleasure, his own credit, and his own twenty things, his own hundred things, which he setteth up, as idols, above Christ!
Dear sir... make Christ yourself, and [acquaint] your love and your heart with the Lord. Stand now by Christ and his truth... 
 Adapted from Andrew A. Bonar, Letters of Samuel Rutherford (Oliphant, Anderson & Ferrier,1848), 390-2.