What does Jesus mean by saying we should have faith and not doubt?

In Matthew 21:21-22, Jesus emphasizes the transformative power of faith when He tells His disciples that if they have faith and do not doubt, they can perform incredible acts, such as removing mountains. This teaching illustrates that true faith rests in God's sovereignty and power rather than in our own limitations. Having faith without doubt means trusting wholeheartedly in Christ’s ability to fulfill His promises and recognizing that all answered prayers align with His will. Such faith is not merely a mental ascent but is deeply rooted in understanding God's character and covenant promises. The implication is that when we approach God in prayer with firm faith, believing that He is able to do exceeding abundantly above all that we ask or think, we can find assurance in His grace and purpose for our lives.