Luke 5:11 KJV
And when they had brought their ships to land, they forsook all, and followed him.
Luke 5:28 KJV
And he left all, rose up, and followed him.
Two times in this chapter we find the report that someone forsook all or left all to follow the Lord. Previous to this Simon and James and John had become disciples of Christ. But a new thing happens here. It is not until this chapter that they gave up the old man to follow the Lord. They had, as it were, attempted to put new wine in their old bottle and it wasn't working. Not until they forsook all could they truly follow Christ.
So could they be genuine believers without forsaking all?
The Bible says in John 6 that when Jesus had preached His hard sayings everyone forsook Him. Everyone except those who had forsaken all.
We cannot serve two masters.
We must forsake all that we cling to in this world if we would follow Christ into the next.