When doing a study on forgiveness in the Bible, one must take into account the whole of Scripture, so that we might have a harmonization on what it is & how to give it & receive it. This is one way we can avoid the one verse theology method of interpretation or quoting verses out of their context.
In the whole topic of forgiveness, there is only one sin that is not forgivable in this age & in the next one: blasphemy of the Holy Spirit. Just something to keep in mind. All other sins are forgivable.
Forgiveness plays a key role in affecting how we are able to express love. (Luke 7:36-50; I Cor 13). "Love...keeps no account of wrongs."
We are to forgive others JUST AS CHRIST HAS FORGIVEN US. Each time we come to the Lord & confess our sins, He is faithful & just, to forgive us our sins & to cleanse us from all unrighteousness. (I John 1:9). Notice that Christ not only forgives us of our sins but ALSO cleanses us from all unrighteousness, all uncleanness. He forgives every time.
We may have residue from the incident: emotional, physical, spiritual, psychogical--yet God can deliver & heal us. Other passages talk about God forgiving the GUILT of our sins, which can cripple some.
Also if we forget we have been cleansed of our past sins, it can keep us from being fruitful & effective in our lives, as the Apostle Peter warns us.
2 Pet 1:3-9 His divine power has given us everything we need for life & godliness through the knowledge of Him who called us by His own glory & excellence.
4Through these He has given us His precious & magnificent promises, so that through them you may become partakers of the divine nature, now that you have escaped the corruption in the world caused by evil desires.
5For this very reason, make every effort to add to your faith virtue & to virtue, knowledge & to knowledge, self-control & to self-control, perseverance & to perseverance, godliness & to godliness, brotherly kindness & to brotherly kindness, love.
8For if you possess these qualities & continue to grow in them, they will keep you from being ineffective & unproductive in your knowledge of our Lord Jesus Christ.
9But whoever lacks these traits is nearsighted to the point of blindness, having FORGOTTEN that he has been cleansed from his PAST SINS.
But back to the OP's questions on Matt 6:14.
"What does this mean exactly? - Does it mean you will lose your salvation or just hinder your walk with God?"
To quickly answer your questions: no and yes. The incident in I Cor chapter 5 shows the sin could have led to physical death but that his spirit would be saved at the day of Jesus Christ. He did repent (2 Cor 1) & so didn't face death right away. Even though Saul in the OT sinned against the commandment of God & led to his being removed as king & also led to his death, he did go to Abraham's Bosom with Samuel.
Yet there are consequences for unrepentant sin in our lives on this earth. A person's physical, mental health & spiritual health is directly affected.
The appearance of the prophet Samuel (God allowed this as a unique incident) from Sheol reiterated God's judgment on the earth of removing his kingship & prophesied of Saul's death the following day. However, he said that Saul would be WITH SAMUEL in Sheol after he & his son were killed.
Samuel was in the believers' compartment in Sheol called Abraham's Bosom or Side or Paradise as Jesus called it also & also called the garden of Eden (you probably wondered where it went) in the prophets (Jeremiah, Ezekiel). The Jews called it Gan Eden or the Abode of Bliss & were familiar with the other title of Abraham's Bosom in Jesus' day.
This verse has an immediate context & is found in the Sermon on the Mount. This is commands for kingdom living where the King is reigning. This is holy living in the Presence of the One Who is holy, dwelling among us.
The wilderness church or congregation was a symbolic picture of the NT church & served as a warning to us. (I Cor 10:1-13) One person's sin affects the whole congregation because we are one body, one assembly.
Josh 7:1-26 This refers to Achan hiding some of the devoted things & lying about it. There was sin in the camp & Israel was being defeated before its enemies. God cannot tolerate sin in the camp nor the kingdom where He is reigning in holiness. It affects the whole congregation & assembly.
Josh 22:9-30 (especially vs 17,18,20: Was not the sin of Peor enough for us, from which we have not cleansed ourselves to this day? It even brought a plague upon the congregation of the LORD.
18And now, would you turn away from the LORD? If you rebel today against the LORD, tomorrow He will be angry with the whole congregation of Israel. Was not Achan son of Zerah unfaithful regarding what was set apart for destruction, bringing wrath upon the whole congregation of Israel? Yet it was not only Achan who perished because of his sin!’”)
Deut 17:1 "You will not sacrifice to the LORD your God an ox or a sheep which has a blemish or any defect, for that is a detestable thing to YHWH your God.
The reason the animal sacrifices had to be without blemish was that they represented, though imperfectly, the Lord Jesus. As Jesus was without blemish, so too, the OT sacrifices had to be without blemish.
Mt 6:1-18 Be careful not to perform your righteous acts before men to be seen by them. If you do, you will have no reward from your Father in heaven.
2So when you give to the needy, do not sound a trumpet before you, as the hypocrites do in the synagogues & on the streets, to be praised by men. Truly I tell you, they already have their full reward.
3But when you give to the needy, do not let your left hand know what your right hand is doing,
4so that your giving may be in secret. And your Father, who sees what is done in secret, will reward you.
5And when you pray, do not be like the hypocrites. For they love to pray standing in the synagogues & on the street corners to be seen by men. Truly I tell you, they already have their full reward.
6But when you pray, go into your inner room, shut your door & pray to your Father, who is unseen. And your Father, who sees what is done in secret, will reward you.
7And when you pray, do not babble on like pagans, for they think that by their many words they will be heard.
8Do not be like them, for your Father knows what you need before you ask Him.
9So then, this is how you should pray: ‘Our Father in heaven, hallowed be Your name,
10Your kingdom come, Your will be done, on earth as it is in heaven.
11Give us this day our daily bread.
12And forgive us our debts, as we also have forgiven our debtors.
13And lead us not into temptation, but deliver us from evil.’
14For if you forgive men their trespasses, your Heavenly Father will also forgive you.
15But if you do not forgive men their trespasses, neither will your Father forgive yours.
16When you fast, do not be somber like the hypocrites, for they disfigure their faces to show men they are fasting. Truly I tell you, they already have their full reward.
17But when you fast, anoint your head and wash your face,
18so that your fasting will not be obvious to men, but only to your Father, who is unseen. And your Father, who sees what is done in secret, will reward you.
Mt 7:2 For with the same judgment you pronounce, you will be judged & with the measure you use, it will be measured to you.
Mt 18:35 That is how My Heavenly Father will treat each of you unless you forgive your brother from your heart."
Mk 11:25 And when you stand to pray, if you hold anything against another, forgive it, so that your Father in heaven will forgive your trespasses as well."
Lk 6:37 Do not judge & you will not be judged. Do not condemn & you will not be condemned. Forgive & you will be forgiven.
Eph 4:32 Be kind & tender-hearted to one another, forgiving each other just as in Christ God forgave you.
Col 3:13 Bear with each other & forgive any complaint you may have against one another. Forgive as the Lord forgave you. (to be continued)