Concerning Jude 1:3:
“Beloved, doing all diligence to be writing to you concerning the common salvation, I have had necessity to write to you entreating to be contending for the faith once being given to the saints.”
Jude calls this people “beloved”, a word of endearment, not just a casual interest or passing contact. These people are important to Jude.
He was diligent, not casual or happenstance, in his writing to the saints who would receive his letter. The Greek word, spouden, means either diligence or haste. Jude urgently wrote to these people; he got to the business that he felt was important.
The initial purpose of his letter was to write to them “concerning the common salvation”. “The”: there is exactly and only one salvation; one Means and one outcome thereby.
This salvation was and is that which is “common” – koinos – held among the entire community of faith, offered to all as the means of entrance into that community, through the washing from sins provided by faith in the shed blood of Christ on our behalf and His resurrection for our life. “The faith” is that belonging to the general population of all who, having heard, have responded to the good news with belief in the facts and trust toward the Saviour to Whom they pertain.
Jude was pressed also, that urging them to “contend earnestly” for that faith was imperative. ἐπαγωνίζομαι – epagonizomai – to strive, provides the image of hard work, struggle, toil, and potentially, distress in that effort. This is not the casual believing, or affirming of belief, but the deliberate and diligent presentation and defence of the truth that God has provided concerning “the faith” that is the sole means of salvation of the souls of sinful men. As Paul affirmed that there is “One body, and one Spirit, even as ye are called in one hope of your calling; One Lord, one faith, one baptism, one God and Father of all …” Ephesians 4:4-6(a)
If all men are under the curse of death for their sin, and God has provided only one means of escaping that curse, expressed by “the faith” by which all men must be saved, if we are to be saved at all, then all other presentations of “faith” or alternative “gospels” are lies that may comfort the mind of the deluded, but leave them dead in their sins and bound for everlasting condemnation, separated from God Which is the source of all goodness and light, joy and peace, love and beauty. Instead of forgiveness and restoration, all who profess a different “faith” will bear their sins in shame, losing the offered opportunity of reconciliation with God, while gaining everlasting torment in that place where God’s perfect attributes will be entirely absent forever.
And anyone bringing the words of another “faith” is a deceiver to be reprimanded, corrected, and if they refuse to submit to the clear word of the Gospel, as delivered by Christ to His faithful apostles, then they are to be rejected and exposed as false professors of a false “faith” that leads not to life, but to death. This presentation and defence of the Gospel, and the correction and rebuke, rejection and exposure of those teaching falsely, are the hard work, or earnest contention, which Jude felt compelled of necessity to urge those who were then, and by extension, are presently, “kept for Jesus Christ”, to engage.