I guess you only have to have Jesus working in your life to know He lives and lives perfectly but knowing He died is powerful because that means He must also have risen and God must therefore have found His life on Earth sinless and His sacrificial death complete to have raised Him. History tells us He was baptised by John the Baptist and tried under Pontius Pilate. Jesus Himself tells us (in The Book of Revelation) that He died and lives forever. Believing Him is crucial to our wellbeing and life in Him because it opens up the possibility He can be effective as our Great High Priest and make us ethically clean. Believing is prerequisite to receiving.
