Albert Barnes on Matthew 28:17

They worshipped him. Paid him honour as the Messiah.

But some doubted. As, for example, Thomas, (Jn 20:25.) The disciples had not expected his resurrection; they were therefore slow to believe. The mention of their doubting shows that they were honest men--that they were not easily imposed on--that they had not previously agreed to affirm that he had risen--that they were convinced only by the strength of the evidence. Their caution in examining the evidence; their slowness to believe; and their firm conviction after all their doubts, and their willingness to show their conviction, even by their death, is most conclusive proof that they were not deceived in regard to the fact of his resurrection.

(p) "they saw him" Mt 16:28