Night and day - Constantly.
Praying exceedingly - Greek, abundantly; that is, there was much more than ordinary prayer. He made this a special subject of prayer; he urged it with earnestness, and without intermission; compare 1 Thessalonians 2:17.
And might perfect that which is lacking in your faith - Might render it complete, or fill up anything which is missing. The word used here (καταρτίσαι katartisai), means, properly, to make fully ready, to put full in order, to make complete; see the Romans 9:22 note; 2 Corinthians 13:9 note; Galatians 6:1 note. It is rendered mending, Matthew 4:21; Mark 1:19; perfect and perfected, Matthew 21:19; Luk 6:40; 2 Corinthians 13:11; 1 Thessalonians 3:10; Heb 13:21; 1 Peter 5:10; fitted, Romans 9:22; perfectly joined together, 1 Corinthians 1:10; restore, Galatians 6:1; prepared, Hebrews 10:5; and framed, Hebrews 11:3. It is not elsewhere used in the New Testament. The meaning here is, that whatever was deficient in their views of religious doctrine the apostle desired to supply. It is to be remembered that he was with them but a comparatively short time before he was compelled to depart to Berea, and it is reasonable to suppose that there were many subjects on which he would be glad to have an opportunity to instruct them more fully.