John Calvin Commentary Acts 2:26

"Therefore my heart was glad, and my tongue rejoiced; Moreover my flesh also shall dwell in hope:" — Acts 2:26 (ASV)

For this my heart rejoiced. Joy of the soul, gladness of the tongue, and quietness of the whole body follow from sure hope and confidence. For unless people are quite past feeling, they will inevitably be anxious and sorrowful, and consequently, miserably tormented, as long as they feel themselves lacking God's help.

But that sure trust which we place in God not only delivers us from anxiety but also fills our hearts with wonderful joy and gladness. That is the joy which Christ promised to his disciples would be full in them, and which he testified could not be taken from them (John 16:22; John 17:13). He expresses the greatness of the joy when he says that it cannot be kept in, but that it will break forth into the gladness of the tongue.

כבוד, indeed, signifies glory, but it is taken in that place, as in many others, to mean the tongue. And so the Greeks have truly translated it this way. The rest of the flesh signifies the quietness of the whole person, which we have through God's protection.

Neither is this any hindrance, because the faithful are continually unsettled and tremble; for as in the midst of sorrows they nevertheless rejoice, so there are no troubles so great that can deprive them of their rest. If anyone objects that the peace of the faithful consists in the spirit, and that it is not in the flesh, I answer that the faithful do rest in body; not because they are free from troubles, but because they believe that God cares for them completely, and that not only their soul will be safe through his protection, but their body also.