Haydock Catholic Bible Commentary
1Co 16:1 . Paul had been charged by the apostles at the council of Jerusalem, to collect alms from the faithful of other Churches, for their poor brethren in Palestine. The apostle acquitted himself of his commission with the greatest possible zeal, and he wishes in this chapter to excite the Corinthians to a like generous conduct with the Galatians: (Calmet) a pastoral ordinance this for alms-deeds, which should be prompt, free, and proportionate to our means. It is just to prefer the wants of the children of the Church to others, particularly in those places whence the light of faith has been received, Jerusalem and Rome.
On the  first day of the week, which is Sunday, and our sabbath, not the Jewish sabbath, as St. John Chrysostom observes, so that before this time, the apostles had appointed the first day of the week for the worship of God. (Witham)
Per unam, that is primam Sabbati, Greek: eis mian sabbaton. St. John Chrysostom, Greek: om. m., toutesti kuriaken, p. 530.
Now I will come. St. Paul came to Corinth a year after he had written this epistle. Titus, his favourite disciple, arrived at Corinth before St. Paul, and was received with the greatest marks of esteem: by him he sent his second epistle to the Corinthians. (Calmet)
A gate is opened to me, large and evident; that is, a fair and good occasion of labouring to convert many, where there are many adversaries. (Witham) --- The work of God is carried on by the power of the cross, and in the midst of contradictions and persecutions. If we suffer this to damp our courage, we forget that we are ministers of a crucified master, and ought to wear his livery.
As to our brother. St. Paul here made an apology for sending Timothy to them, who was a young man, and not so renowned for eloquence and sanctity as Apollo, informing them that Apollo did not wish to come, perhaps on account of the commotions that were at Corinth at his account. (Estius)
1Co 16:13 Christian is a soldier, environed and attacked on all sides by enemies. It is his duty to guard against surprise. He should never abandon the post of faith, nor the fortress of the Church, unless he wish to fall an easy prey to his adversaries. He should fight with courage, and after each attack, carefully repair the breaches made by the enemy, that he may be in a condition to sustain fresh attacks by charity, which is the principle, the soul, the life, and heart of our every action.
The first-fruits fo Achaia; the first there converted. (Witham)
Which was wanting on your part, they have supplied, by informing me, and giving me a full account of all. (Witham)
Let him be anathema, accursed. Maran Atha, which, according to St. Jerome and St. John Chrysostom, signify, the Lord is come already, and so is to be taken as an admonition to those who doubted of the resurrection, and is to put them in mind, that Christ, the Judge of the living and the dead, is come already. The Rabbinical writers tells us, there are three curses among the Jews called by different names: that the first was niddui, which implied an expulsion from the synagogue for a time; the second was greater, such being quite cut off from the common society, called Cherem; the third, Maran Atha, the Lord cometh, is coming, or is come, which was followed by exemplary judgments and punishments. Thus Mons. Hure, in his Bible Dictionary, Mr. Legh, in his Critica Sacra, and also Mr. Nary. But whether this is better grounded than many other Rabbinical stories, let others judge. (Witham)
Maran Atha, Greek: maran atha. St. John Chrysostom, Greek: ti de esti maran atha; o kurios emon elthe, &c. St. Hierom [St. Jerome], Epist. ad Marcellam. tom. ii. p. 706, and de nominibus Hebraicis. tom. iv. p. 78.
1Co 16:24 , thrice happy the pastor, whose life, labours, zeal, and the testimony of his own conscience, embolden him to say with St. Paul, that he loves the flock of Jesus Christ, that he only loves them for Jesus Christ, and in Jesus Christ, by virtue of the Holy Spirit.