Of his four sons, Felix, William, Jabez, and Jonathan, Carey's correspondence was most frequent at this period with William, who went forth in 1807 to Dinapoor to begin his independent career as a missionary by the side of Fernandez.
"2nd April 1807.—We have the greatest encouragement to go forward in the work of our Lord Jesus, because we have every reason to conclude that it will be successful at last. It is the cause which God has had in His mind from eternity, the cause for which Christ shed His blood, that for which the Spirit and word of God were given, that which is the subject of many great promises, that for which the saints have been always praying, and which God Himself bears an infinite regard to in His dispensations of Providence and Grace. The success thereof is therefore certain. Be encouraged, therefore, my dear son, to devote yourself entirely to it, and to pursue it as a matter of the very first importance even to your dying day.
"Give my love to Mr. and Mrs. Creighton and to Mr. Ellerton, Mr. Grant, or any other who knows me about Malda, also to our native Brethren."
"CALCUTTA, 29th September 1808.—A ship is just arrived which brings the account that Buonaparte has taken possession of the whole kingdom of Spain, and that the Royal family of that country are in prison at Bayonne. It is likely that Turkey is fallen before now, and what will be the end of these wonders we cannot tell. I see the wrath of God poured out on the nations which have so long persecuted His Gospel, and prevented the spread of His truth. Buonaparte is but the minister of the Divine vengeance, the public executioner now employed to execute the sentence of God upon criminal men. He, however, has no end in view but the gratifying his own ambition."
"22nd December 1808.—DEAR WILLIAM—Be steadfast...Walk worthy of your high calling, and so as to be a pattern to others who may engage in similar undertakings. Much depends upon us who go first to the work of the Lord in this country; and we have reason to believe that succeeding Ministers of the Gospel in this country will be more or less influenced by our example...All, even the best of men, are more likely to be influenced by evil example than benefited by good: let it, therefore, be your business and mine to live and act for God in all things and at all times.
"I am very glad you wrote to Jabez and Jonathan. O that I could see them converted!"
"30th May 1809.—When you come down take a little pains to bring down a few plants of some sort. There is one grows plentifully about Sadamahal which grows about as high as one's knee, and produces a large red flower. Put half a dozen plants in pots (with a hole in the bottom). There is at Sadamahal (for I found it there) a plant which produces a flower like Bhayt, of a pale bluish colour, almost white; and indeed several other things there. Try and bring something. Can't you bring the grasshopper which has a saddle on its back, or the bird which has a large crest which he opens when he settles on the ground? I want to give you a little taste for natural objects. Felix is very good indeed in this respect."
"26th April 1809.—You, my dear William, are situated in a post which is very dear to my remembrance because the first years of my residence in India were spent in that neighbourhood. I therefore greatly rejoice in any exertions which you are enabled to make for the cause of our Redeemer...Should you, after many years' labour, be instrumental in the conversion of only one soul, it would be worth the work of a whole life...I am not sure that I have been of real use to any one person since I have been in this country, yet I dare not give up the work in which I am engaged. Indeed, notwithstanding all the discouragements which I feel from my own unfitness for any part of it, I prefer it to everything else, and consider that in the work of my Redeemer I have a rich reward. If you are enabled to persevere you will feel the same, and will say with the great Apostle—'I count not my life dear to me that I may fulfil the ministry which I have received of the Lord.' 'Unto me is this grace (favour) given that I should preach among the Gentiles the unsearchable riches of Christ.' Hold on, therefore, be steady in your work, and leave the result with God.
"I have been thinking of a mission to the Ten Tribes of Israel, I mean the Afghans, who inhabit Cabul...I leave the other side for your mother to write a few lines to Mary, to whom give my love."
"CALCUTTA, 1st November 1809.—Yesterday was the day for the Chinese examination, at which Jabez acquitted himself with much honour. I wish his heart were truly set on God. One of the greatest blessings which I am now anxious to see before my death is the conversion of him and Jonathan, and their being employed in the work of the Lord.