Albert Barnes Presbyterian @notesbybarnes

Verse 66. Sealing the stone. The sepulchre was made sure, by affixing the large stone to the entrance in such a way that it could not be removed without detection. It was sealed. In what way this was done cannot now be certainly told.

Jamieson-Fausset-Brown Reformed @jfbcommentary

So they went, and made the sepulchre sure, sealing the stone--which Mark (Mar 16:4) says was "very great." and setting a watch--to guard it. What more could man do? But while they are trying to prevent the resurrection of the Prince of Life, God makes use of their precautions for His own ends.