To me, this is why I said, once a person believes in Jesus as what he have said in the scriptures, and he knows whoever is faithful and doing the works until the end of time.
Blessed is that servant, whom his lord when he cometh shall find so doing. Matthew 24:46
http://biblehub.com/matthew/24-46.htm
John 7:38 This is from The Adam Clarke Commentary
He that believeth on me, as the Scripture hath said - He who receives me as the Messiah, according to what the Scripture has said concerning me; my person, birth, conduct, preaching, and miracles, being compared with what is written there as ascertaining the true Messiah. Out of his belly - from his heart and soul; for in his soul shall this Spirit dwell.
Living water - As a true spring is ever supplied with water from the great deep, with which it has communication, so shall the soul of the genuine believer be supplied with light, life, love, and liberty, and all the other graces of the indwelling Spirit, from the indwelling Christ.
The below, Which maybe hard to grasp wright now for some people, because of Jesus customs:
Living Water: The below is talking about The Feast of Tabernacles in verse 37, but verse 38. Is talking about how a person believes in Christ at that time of the feast season, for those that have that spirit of the feast.
37 In the last day, that great day of the feast, Jesus stood and cried, saying, If any man thirst, let him come unto me, and drink. 38 He that believeth on me, as the scripture hath said, out of his belly shall flow rivers of living water. 39(But this spake he of the Spirit, which they that believe on him should receive: for the Holy Ghost was not yet given; because that Jesus was not yet glorified.)
The Jews frequently compare the gifts and influences of the Holy Spirit to water in general - to rain, fountains, wells, rivers, etc., etc. The Scriptures abound in this metaphor.
Psalm 36:8, Psalm 36:9; Isaiah 44:3, Isaiah 44:4; Joel 2:23.