An excerpt from one of my favorite theology books, John L. Dagg’s Manual of Theology.
DUTY OF GRATITUDE FOR DIVINE GRACE.
As love is the affection which should arise in our hears, from a view of God’s character, so gratitude is the affection which should be produced, by a view of the benefits that he confers. The stream of his benefits flows incessantly so that our cup is ever full. To receive the benefits thoughtlessly, like the brutes that perish, and to enjoy them without thanksgiving to him from whom they come, is demonstration complete of human depravity. Such demonstration is given daily and hourly in the conduct of mankind, and by it God is offended and his wrath provoked. The unthankful man is the evil man, and the enemy of God. Hence, when we are called on to love our enemies, the example proposed for our initiation is the bestowment of God’s providential blessing on the unthankful.
Love your enemies, and do good, and lend, hoping for nothing again, and your reward shall be great, and ye shall be the children of the Highest; for He is kind unto the unthankful and to the evil.
We are bound to thank God for the blessings of providence so incessantly and so richly bestowed; but far higher obligations to gratitude, arise from the grace that bringeth salvation. This grace includes God’s gift of his Son, a gift so great that no name for it can be found. “God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.” The love of the Son, which demands our gratitude, is not less unmeasured, than the love of the Father: whence Paul labored to explore “the height, the length, the breadth and the depth of the love of Christ, which passeth knowledge.” And our gratitude is not complete till we acknowledge and celebrate also the love of the Spirit, by whom believers are fitted for the enjoyment of God, and brought into fellowship with him.
In exercising and cultivating our gratitude for the blessings of salvation, we must distinctly recognise that they come from God, and that they are intentionally bestowed. When we trace them to their source, the infinite love of the triune God; and when we receive them, as conferred according to his eternal counsel, we are prepared while we enjoy the benefit, to return thanks to its Author, and to exclaim with liveliest emotion, “Bless the Lord, O my soul, and forget not all his benefits.”
That our gratitude to God may be proportional to the blessing received, we should count his mercies over, and survey their magnitude. Unmeasurable! unspeakable! passing knowledge!–yet we should labor to know them; and as we make progress in this spiritual knowledge, our gratitude should swell and fill the enlarged capacity of the mind.
In order to the full exercise of gratitude to God it is necessary to be thoroughly impressed with the conviction that the blessings received are wholly undeserved, and proceed entirely from the mere mercy and grace of God. When we feel that we are less than the least of all God’s mercies, that our only desert is hell, and that if salvation is bestowed on us, it will be of his own good pleasure; we are prepared to give thanks for the unspeakable gift, and to say, “Not unto us, O Lord, not unto us, but unto thy name give glory.”
 2 Thess. ii. 13. We are bound to thank God always for you, brethren, beloved of the Lord, because God hath from the beginning chosen you to salvation, through sanctification of the Spirit and belief of the truth.
1 Cor. xv. 10. By the grace of God, I am what I am.
2 Cor. ix. 15. Thanks be to God for his unspeakable gift.
 Luke vi. 25.
 Tit. ii. 11.
 John iii. 16.
 Eph. iii. 18, 19.
 Rom. xv. 30.
 Ps. ciii. 2.
 Ps. cxv.