Hello Drich, this is off-topic (as Matthew 5:13 concerns Christian living, service, fighting the good fight in this life, etc., not soteriology), so I'll try to keep it short 
As for the idea of Christians not being saved until the Judgment (rather than when we first come to saving faith and are justified by God), what do we do then with the verses that say otherwise? For instance, here's something from the Lord Jesus that speaks to this directly (and that in several different ways).
John 5
24 Truly, truly, I say to you, he who hears My word, and believes Him who sent Me, ~has~ eternal life, and does not come into judgment, but has passed out of death into life.
You know, I think that I'd better end this right here (even though there is more that I'd like to discuss with you, as I don't want to derail @God-fearing's thread). In fact, I think that this topic is worthy of its own thread. Would you be interested in that idea by any chance?
Thanks 
God bless you!!
~Deuteronomy
1 John 5
11 The witness is this, that God has given us eternal life, and this life is in His Son.
12 He who has the Son has the life; he who does not have the Son of God does not have the life.
13 These things I have written to you who believe in the name of the Son of God, in order that you may ~know~ that you have eternal life.
There are two potential conflicts as you have pointed out here. verse 12 He who has the son has eternal life.
and the word judgement here in your translation leaves the interpretation of the word "judgement" to the reader.
However the word judgement in this passage is not so ambiguous in other translations. For example in the KJV the greek word for judgement (Krisis) is translated condemnation. while condemnation can mean judgement/Evalutation it's contextual meaning has to do with Sentencing. Example: "Your Judgement for your guilty verdict is 5 years hard labor"
John 5: KJV:Verily, verily, I say unto you, He that heareth my word, and believeth on him that sent me, hath everlasting life, and shall not come into condemnation; but is passed from death unto life.
Meaning the word judgement does not focus on the evaluation potion of judged, but rather the punitive side of judgement Eg your sentence or final "judgment."
The word phrase "Has eternal life." out of context would allow one to assume that the judgement for eternal life has already been made. However once you reframe those two words back into the context of scripture we see that the "eternal life" one has been promised is conditional. The condition that have to be met are 1. You must believe (not just acknowledge but act on said beliefs) That Jesus is the one and only son of God and you must believe in the Father who sent Him. Belief meaning we must follow and do what they say do, not just acknowledge them.
Without these two beliefs requiring action, we do not have the promise of eternal life. Judgement day is the time that has been allocated to determine whether or not you have met the requirements of eternal life.
21 “Not everyone who says to me, ‘Lord, Lord,’ will enter the kingdom of heaven, but only the one who does the will of my Father who is in heaven. 22 Many will say to me on that day, ‘Lord, Lord, did we not prophesy in your name and in your name drive out demons and in your name perform many miracles?’ 23 Then I will tell them plainly, ‘I never knew you. Away from me, you evildoers!’
Why? Because again Salvation is not a work we do but a gift from Jesus, that He decides who is to receive this gift. Again look at mat 7:
These men on the day of judgement where fully convinced of their salvation. They like john 5 said confessed with their mouth when they cried out "Lord, Lord" That Jesus was Lord and did many good works in the church from prophesying to driving out demons, yet on the day of judgement Jesus says I NEVER knew you.
Because again, our salvation is not dependent on our efforts OR Our Beliefs. Our Salvation is 100% Dependent on the judgement of Christ. as NO ONE enters the kingdom but through Him. Meaning No one enters the Kingdom because of what church they sat in, what creed they professed, what prayer they prayed, what baptism the took etc etc.. We Enter through the judgement of Christ.