All sciences have tools or documented comparisons so any device or formula can be calibrated against a proven measure or standard. The reality of bible salvation is based on a series of promises and actions which God has promised through His Holy Spirit, of which He confirms. God is well aware of human failure and has thus calibrated His word and blessings with signs and evidence outside of intellectual and emotional factors alone. Like the Prime Meridian (the 0 degree line of longitude) used for all charting and travelling on the earth's surface, the church needs a fixed starting point of reference, or natural wisdom will corrupt spiritual truths.