John Calvin Commentary Acts 9:40

"But Peter put them all forth, and kneeled down and prayed; and turning to the body, he said, Tabitha, arise. And she opened her eyes; and when she saw Peter, she sat up." — Acts 9:40 (ASV)

When they were all put forth. When he takes time to pray, he still seems to doubt what the outcome will be. When he healed Aeneas, he broke out into these words without any pause, Aeneas, Jesus Christ make you whole. But as the Spirit's operation is not always the same, it may be that even though he knew God's power, he still approached the miracle by degrees.

Yet it seems to be an absurd thing that he puts all the saints out of the chamber, for whom it would have been better to have seen it with their own eyes. But because the Lord had not yet revealed when and how He would show forth His power, he desired to be alone so that he might pray more suitably.

Also, it might be that he knew some other reason that moved him to do this, which we do not know. It is recorded in the Sacred History (1 Kings 17:23) that Elijah did the same. For he, being alone, without even the child's mother with him, does stretch himself three times upon the dead corpse.

For the Spirit of God has His strong impulses, which, if anyone tries to judge by ordinary human standards or measure by carnal understanding, they will act wickedly and unjustly. We must think this: when Peter, as if doubting, seeks a private place, he prevents superstition, lest anyone should ascribe God's work, of which he was only a minister, to his own power. For he who withdrew from company and prayed so earnestly, plainly confessed that the matter was not in his own hand. Therefore, when Peter wishes to know what pleases the Lord, he confesses that the Lord alone was the author of the work.

Kneeling in prayer is a sign of humility, which has a double benefit: all our members may be applied to the worship of God, and the body's external exercise may help the mind's weakness. But we must take care, as often as we kneel, that the heart's inward submission corresponds to the ceremony, so that it is not vain and false.

Turning towards the corpse. This also seems contrary to reason, that he speaks to a corpse without feeling; but this speaking to the dead corpse was one aspect of the intensity to which the Spirit of God compelled Peter. And if anyone desires a reason, this form of speech more vividly expresses God's power in raising the dead than if it were said in the third person, “Let this body receive life again and live.” Therefore, when Ezekiel represents the deliverance of the people under the figure of the resurrection:

“O dead bones,” he says, “hear the word of the Lord,” (Ezekiel 37:4).

And Christ says, “The time shall come when the dead shall hear
the voice of the Son of God,” (John 5:25).

For this was indeed the voice of Christ, which was uttered by Peter's mouth, and gave breath back to Tabitha's body. The circumstances that follow serve to confirm the certainty of the miracle.