Salvation in both the OT and NT has always been conditional upon obedience. Even in the OT, though the Jews were God's chosen they still had to be obedient to God which they were not, hence cast off (Rom 11). IF salvation were uncondtional then all men would unconditionally be saved (Tts 2:11)Not salvation. It is ALL a gift from God, and not from you, AT ALL (Eph2:8-9).
You reading your presuppositions into scripture.
Salvation and faith are gifts - you can't buy them because you don't have currency.
One is saved by Christ's righteousness.
Tons of examples from the Bible of God's free gifts being conditional. Already gave you one with Naaman. Another is Noah, (Heb 11) by faith Noah moved with fear prepared an ark in the saving of his house. The saving of Noah's house was a free gracious gift of God for God certainly did not owe that to Noah. Yet it took Noah's obedience in building the ark to receive that free gift of God and his obedience to God earned him nothing but just meeting a necessary condition God placed upon His free gift.
One cannot buy salvation with money but one can meet the necessary condition of obedience God has placed upon the free gift of salvation. Again, Jn 3:16 for God so loved the world He GAVE His only begotten Son. The word 'gave' means Christ was a free gift God gave to the world for God sure did not owe the world the gift of a Saviour. But in order to be saved by that free gift of the Christ requires one to meet the condition in obeying Christ (Heb 5:9). Again, obedience earns nothing (Luke 17:7-10)