From Of First Importance, "The Excellency of Election":
“Oh the excellency of the doctrine of election, and of the saints’ final perseverance, to those who are truly sealed by the Spirit of promise! I am persuaded, till a man comes to believe and feel these important truths, he cannot come out of himself; but when convinced of these, and assured of the application of them to his own heart, he then walks by faith indeed, not in himself but in the Son of God, who died and gave himself for him. Love, not fear, constrains him to obedience.”
From The Purpose Driven Blog, a selection from Whitefield's "The Lord Our Righteousness":
Whoever is acquainted with the nature of mankind in general, or the propensity of his own heart in particular, must acknowledge, that self- righteousness is the last idol that is rooted out of the heart: being once born under a covenant of works, it is natural for us all to have recourse to a covenant of works, for our everlasting salvation. And we have contracted such devilish pride, by our fall from God, that we would, if not wholly, yet in part at least, glory in being the cause of our own salvation. We cry out against popery, and that very justly; but we are all Papists, at least, I am sure, we are all Arminians by nature; and therefore no wonder so many natural men embrace that scheme. It is true, we disclaim the doctrine of merit, are ashamed directly to say we deserve any good at the hands of God; therefore, as the Apostle excellently well observes, "we go about," we fetch a circuit, "to establish a righteousness of our own, and," like the Pharisees of old, "will not wholly submit to that righteousness which is of God through Jesus Christ our Lord."
From DG, "Whitefield Exalts in Christ":
The Lord, the Lord Christ, the everlasting God, is your righteousness. Christ has justified you, who is he that condemneth you? Christ has died for you, nay rather is risen again, and ever liveth to make intercession for you. Being now justified by his grace, you have peace with God, and shall, ere long, be with Jesus in glory, reaping everlasting and unspeakable fruits both in body and soul. For there is no condemnation to those that are really in Christ Jesus. Whether Paul or Apollos, or life or death, all is yours if you are Christ's, for Christ is God's.
My brethren, my heart is enlarged towards you! O think of the love of Christ in dying for you! If the Lord be your righteousness, let the righteousness of your Lord be continually in your mouth. Talk of, O talk of, and recommend the righteousness of Christ, when you lie down, and when you rise up, at your going out and coming in! Think of the greatness of the gift, as well as the giver! Show to all the world, in whom you have believed! Let all by your fruits know, that the Lord is your righteousness, and that you are waiting for your Lord from heaven!
This is not Whitefield, but it's a quote at Unashamed Workman from David Wells that probably describes Whitefield's preaching:
Preaching is not a conversation about some interesting ideas. It is not the moment in which postmoderns hear their own private message in the biblical words, one unique to each one who hears, and then go their own way. No! This is God speaking! He speaks through the stammering lips of the preacher where that preacher’s mind is on the text of Scripture and his heart is in the presence of God. God, as Luther puts it, lives in the preacher’s mouth.
This is the kind of preaching that issues a summons, which nourishes the soul, which draws the congregation into the very presence of God so that no matter what aspect of his character, his truth, his working in this world is in focus, we leave with awe, gratitude, encouragement, and sometimes a rebuke. We have been in the very presence of God! This is what great preaching always does.