He saw in truth that through the operation of the Holy Spirit, which He gave to the holy Apostles, the acquisition of many would be made, (or that many would be brought to the faith.) He is said therefore to have rejoiced in the Holy Spirit, that is, in the results which came forth through the Holy Spirit. For as one who loved mankind He considered the conversion of sinners to be a subject for rejoicing, for which He gives thanks. As it follows, I give thanks unto thee, O Father.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).