In John 6:16-21, the main theme switches from Christ’s sufficiency to provide all that we need, to trusting that he is sufficient to accomplish his promises according to his perfect plan. Nevertheless, we can become frightened to the point of losing our bearings due to fearful unbelief in how God can fulfill his promises. This includes any situation in which we think God can’t be involved with.
For instance, we might wrongly conclude that God can’t be accomplishing his purposes in a nation or a city that is hell-bent towards evil. Or…”God can’t be up to anything beneficial in my family if at least one person seems to be turning away from the Lord. He can’t work for the spiritual good in the rest of my family with something like that going on.”
Or perhaps…”There’s no way God is working out his sanctification in me during this ongoing health trial. In fact, I can’t even see how this is going to get resolved and I’m too afraid of what might happen to keep handing myself over to God’s promises instead of being anxious about it. These circumstances make me frightened and disillusioned and it wouldn’t be right to just push past my fears, so I better just wait to fully trust in God’s word until I don’t feel as afraid. Besides, surely God’s will wouldn’t seem this scary.”
The disciples had similar fears upon seeing Jesus walking on the water, but he comes to them while reassuring them of his promise to be with them, which is designed to dispel all fears.