Matthew 28:17 contains a detail that is easy to overlook in the resurrection appearance: "And when they saw him, they worshipped him: but some doubted." These are the eleven remaining disciples, in the presence of the resurrected Jesus — and some doubted. The Greek distazantes — doubted — means to stand in two places, to be divided. The worship and the doubt are in the same scene, with the same people, at the same moment. Jesus proceeds to give them the Great Commission without first resolving the doubt.
Hebrews 11:1 — "Now faith is the substance of things hoped for, the evidence of things not seen" — defines faith specifically in terms of what is not visible. The Greek elegchos — evidence — is a legal term for proof. Faith is not the absence of uncertainty; it is the substance and evidence that operates where visibility is absent. Doubt is not the opposite of faith — it is one of the conditions in which faith operates.
Commentary is from a charismatic Protestant perspective, drawing on KJV text and public-domain sources including Spurgeon, Andrew Murray, and Matthew Henry.