The only real objection against OSAS is not salvation... it is sin.
The objection, of course, is that OSAS could be interpreted as a "license to sin."
The objection is that OSAS, related to the doctrine of Sola Fide, effectively separates the
need for one to be righteous and live accordingly in order to enter heaven from being an actual
qualification for entering heaven. With that view, faith, alone, meets that qualification whether as a one-time act or an ongoing act.
Or, to cover all bases, one is said to somehow be made righteous anyway, as a side-benefit of faith/being justified (and not as an integral
part of justification or being made just). A problem in any case is that believers continue to sin, of course.
In the ancient faith, we're justified
unto righteousness now, unto 'slavery to righteousness' (Rom 6), a new righteousness apart from the law that the law and prophets testify to but could never accomplish in us (Rom 3:20-21). So how is a person justified, by simply being forgiven, or also by being given a new righteousness, empowered to sin no more?
“I will put my law in their minds
and write it on their hearts.
I will be their God,
and they will be my people.
No longer will they teach their neighbor,
or say to one another, ‘Know the Lord,’
because they will all know me,
from the least of them to the greatest,”
declares the Lord.
“For I will forgive their wickedness
and will remember their sins no more.” Jer 31:33-34
The counter to OSAS is TLLF - "Twice Lost, Lost Forever." This is commonly heard when quoting Heb 10 as proof against OSAS.
Hebrews 10:26-27 KJV
26 For if we sin wilfully after that we have received the knowledge of the truth, there remaineth no more sacrifice for sins,
27 But a certain fearful looking for of judgment and fiery indignation, which shall devour the adversaries.
Who has not sinned since they were saved?
This is the next logical question, and it's one the church faced and dealt with many, many centuries ago. The early Christians had given up
much in order to convert to the faith, including their lives at times. Becoming Christian was to turn from, to deny, the world and its ways and its sin- and turn to God. To return to sin in a major way: murder, theft, adultery, etc was to turn one’s back on and away from God and His church. As they were quite the rigorists in this observance of the faith, it was considered to be impossible for such a person to return to fellowship again. And passages such as the one you quoted from Heb or Heb 6:4-6 or 2 Pet 2:20-22 or 1 John 5:16-17, etc, only supported such notions which was the standard attitude throughout the various churches throughout the whole church world. But in the 2nd century a bishop, amid
much heated controversy, determined and taught, based on a deeper understanding of God’s mercy and love, that one could repent for
any sin and return to the fold even if much penance and time was required back then. This teaching would eventually become adopted by the whole church.
So, we have these two extremes: of no repentance with forgiveness possible in the early church, to a modern position of virtually taking forgiveness for granted or even being unconcerned with sin at an even greater extreme. The church came to understand and strike a balanced position between these extremes: knowing that absolute perfect sinlessness would be impossible in this life even while that was nonetheless the proper goal, and yet that our striving towards that goal with success, now with the help of grace to overcome egregious sins, sins that will bar us from heaven and sonship of God according to Romans, Galatians, 1 Cor, Revelation, John’s letters, etc, is necessary. To fail to do so means we either haven’t entered any real relationship with Him, or have departed from it.
