In praying, they said. Word for word it is, Having prayed, they said; but there is no obscurity in the sense, because his meaning was to speak as followeth, that they prayed; and yet he doth not reckon up all the words, being content briefly to show the sum. Therefore, although they were both of honest conversation, yea, although they did excel in holiness and other virtues, yet because the integrity of the heart, whereof God is the alone knower and judge, is the chief, the disciples pray that God would bring that to light which was hidden from men. The same ought to be required even at this day in choosing pastors; for howsoever we are not to appoint two for one, yet because we may oftentimes be deceived, and the discerning of spirits cometh of the Lord, we must always pray unto God, that he will show unto us what men he will have to be ministers, that he may direct and govern our purposes. Here we may also gather what great regard we must have of integrity and innocency in choosing pastors, without which both learning and eloquence, and what excellency soever can be invented, are as nothing. [1]

Footnotes

1 - "In fumum abeunt," go to smoke.

And they prayed - As they could not agree on the individual, they invoked the direction of God in their choice - an example which should be followed in every selection of an individual to exercise the duties of the sacred office of the ministry.
Which knowest the hearts of all men - This is often declared to be the special prerogative of God, Jeremiah 17:10, "I, Yahweh, search the heart," etc.; Psalm 139:1, Psalm 139:23; 1-Chronicles 28:9. Yet this attribute is also expressly ascribed to Jesus Christ, Revelation 2:18; compare 23, "These things saith the Son of God - I am he which searcheth the reins and the hearts"; John 2:25; John 6:64; John 16:19. There are strong reasons for supposing that the apostles on this occasion addressed this prayer to the Lord Jesus Christ:
(1) The name Lord - Κύριος Kurios - is the common appellation which they gave to him, Acts 2:36; Acts 7:59-60; Acts 10:36; 1-Corinthians 2:8; Philippians 2:11; Revelation 11:8, et al.
(2) we are told that they worshipped him, or rendered him divine honors after his ascension, Luke 24:52.
(3) the disciples were accustomed to address him after his crucifixion by the names Lord or God indifferently, Acts 1:6; John 20:28; Acts 7:59.
(4) this was a matter pertaining especially to the church which the Lord Jesus had redeemed, and "to his own arrangement" in regard to it. He had chosen the apostles; he had given them their commission; he had fixed their number; and, what is worthy of special remark here, he had been the companion of the very men here designated as candidates for the office, and knew their qualifications for this work. If the apostles ever called on the Lord Jesus after his ascension, this was a case in which they would be likely to do it. That it was done is clear from the account of the death of Stephen, Acts 7:59-60. And in this important matter of ordaining a new apostle to be a witness for Jesus Christ, nothing was more natural than that they should address him, though bodily absent, as they would assuredly have done if he were present. But if on this occasion they did actually address Christ, then two things clearly follow. First, that it is proper to render him divine homage, agreeably to the uniform declarations of the Scripture: John 5:23, "That all men should honor the Son even as they honor the Father"; Hebrews 1:6, "And let all the angels of God worship him"; Philippians 2:10-11; Revelation 5:8-14; 1-Thessalonians 3:11-12. Secondly, he must be divine. To none other but God can religious homage be rendered; and none other can be described as knowing the hearts of all people. The reason why they appealed to him on this occasion as the searcher of the heart was doubtless the great importance of the work to which the successor of Judas was to be called. One apostle of fair external character had proved a traitor; and, with this fact before them, they appealed to the Saviour himself to select one who would be true to him, and not bring dishonor upon his cause.
Show whether - Show which of them.
Thou hast chosen - Which of the two thou hast judged to be best qualified for the work.

Thou Lord, which knowest the hearts - Συ, κυριε, καρδιογνωστα. The word καρδιογνωστης, the searcher of hearts, seems to be used here as an attribute of God; he knows the hearts, the most secret purposes, intentions, and dispositions of all men; and because he is the knower of hearts, he knew which of these men he had qualified the best, by natural and gracious dispositions and powers, for the important work to which one of them was now to be appointed.

And they prayed and said,.... Having proposed the above two persons, and not well knowing which to pitch upon, they being both very agreeable and fit for such service; they chose not to determine the affair without seeking to God for direction; a method to be taken in all cases, and especially in matters of importance: and the substance of their petition, though perhaps not in just the same words, was,
thou, Lord, which knowest the hearts of all men; which is a character peculiar to the one only living, and true God; for none knows the hearts of men, but God, who is the Maker of them; and he knows all the thoughts, counsels, and purposes of them, and the good or bad that is in them:
shew whether of these two thou hast chosen; being desirous of having their choice directed by the choice God had made, in his eternal mind; and which they desired might be signified and pointed out to them, in some way or another, that they might be certain of the mind and will of God, and act according to it.

prayed and said, Thou, Lord, &c.--"The word 'Lord,' placed absolutely, denotes in the New Testament almost universally THE SON; and the words, 'Show whom Thou hast chosen,' are decisive. The apostles are just Christ's messengers: It is He that sends them, and of Him they bear witness. Here, therefore, we have the first example of a prayer offered to the exalted Redeemer; furnishing indirectly the strongest proof of His divinity" [OLSHAUSEN].
which knowest the hearts of all men--See John 2:24-25; John 21:15-17; Revelation 2:23.

They prayed. That the Lord might choose between them. A choice of men for any responsible church work ought to be made with earnest prayer. It is likely that one of the apostles offered the prayer, all joining in the petition.