Speaking in the Gospel of John, Jesus uses a strong affirmation 24 times.
"Vines Expository Dictionary" tells us the Greek word is ALETHOS meaning truly; surely.
Following are the terms used in the five translations that I usually use.
This week I would like to share some of these from the NKJV.
(My suggestion is that each one read the verses in context to know what Jesus is strongly affirming.) "Verily, verily" The King James Version "Most assuredly" The New King James Version "Truly, truly" The New American Standard Bible "I tell you the truth" The New International Version "I assure you most solemnly" The Amplified Bible

Concerning Christ--
His glory:
"And He said to him, 'Most assuredly, I say to you, hereafter you shall see heaven open, and the angels of God ascending and descending upon the Son of Man.'" John 1:51

'His eternity:
"Jesus said to them, 'Most assuredly, I say to you, before Abraham was, I AM.'" 8:58

His uniqueness:
"Most assuredly, I say to you, he who does not enter the sheepfold by the door, but climbs up some other way, the same is a thief and a robber.'" 10:1 "Then Jesus said to them again, 'Most assuredly, I say to you, I am the door of the sheep.'" Vs. 7

His mission:
"Then Jesus said to them, 'Most assuredly, I say to you, Moses did not give you the bread from heaven, but My Father gives you the true bread from heaven. For the bread of God is He who comes down from heaven and gives life to the world.'" 6:32-33

His work lead by God:
"Then Jesus answered and said to them, 'Most assuredly, I say to you, the Son can do nothing of Himself, but what He sees the Father do; for whatever He does, the Son also does in like manner.'" 5:19

His betrayal:
"When Jesus had said these things, He was troubled in spirit, and testified and said, 'Most assuredly, I say to you, one of you will betray Me.'" 13:21

His death:
"Most assuredly, I say to you, unless a grain of wheat falls into the ground and dies, it remains alone; but if it dies, it produces much grain.'" 12:24

Concerning man's--
Spiritual bondage:
Jesus answered them, 'Most assuredly, I say to you, whoever commits sin is a slave of sin.'" 8:34

Spiritual darkness:
"Jesus answered them and said, 'Most assuredly, I say to you, you seek Me, not because you saw the signs, but because you ate the loaves and were filled.'" 6:26

Need of regeneration:
"Jesus answered and said to him, 'Most assuredly, I say to you, unless one is born again, he cannot see the Kingdom of God.'" 3:3 "Jesus answered, 'Most assuredly, I say to you, unless one is born of water and the Spirit, he cannot enter the kingdom of God.'" Vs. 5

Need of salvation:
"Most assuredly, I say to you, he who hears My word and believes in Him who send Me has everlasting life, and shall not come into judgment, but has passed from death into life." 5:24 "Most assuredly, I say to you, the hour is coming , and now is, when the dead will hear the voice of the Son of God; and those who hear will live."
Vs. 25

The means of salvation:
"Most assuredly, I say to you, he who believes in Me has everlasting life."
6:47
"Most assuredly, I say to you, if anyone keeps My word he shall never see death." 8:51

Did you notice the 'I say to you' in these verses? Whether individually or to a group, Jesus is speaking truths to every heart!
Some other 'most assuredly' verses Jesus speaks in the Gospel of John are:
13:16; 13:20; 13:38; 14:12; 16:23; 21:18

Lord Jesus, thank you, for everlasting truth! You are Truth!  'Yes, the same yesterday, and today and forever'! Amen .