One contention in the early church was that unless one was circumcised he could not be saved (Ac.15:1). After the apostles prayed and debated about this it was concluded that circumcision was not necessary. When the doctrine of salvation became clearer in the course of time, Paul stated that it was only by grace through faith (Ep.2:8,9). The implication was that if salvation was by the unmerited favour from God, nothing we could do could qualify us for it or was necessary to add to it (Ro.4:4,5).
But circumcision is not the issue that troubles Christians these days. But haven't you heard people say that unless we are baptised in water in addition to having faith we cannot be saved? They quote Mk.16:16 to prove this. What they don't realise is that the Bible cannot teach one thing in one place and another in another place! When the rest of the New Testament teaches salvation by grace, surely there must be some other meaning to this verse! Especially when the second half of the verse mentions only believing as the thing that avoids condemnation! (There are even some who practically believe that baptism alone will save people. Some 'baptise' babies and others baptise adults and assume that now those are saved!)
For a larger number of people who have been born again through faith a question that still remains is their relationship to keeping God's laws. Surely there are many verses in both the OT and NT that talk about the importance of keeping God's commandments and warning that those who don't keep His commandments are deceiving themselves. How do we understand this rightly?
Salvation is by grace through faith. What exactly is this faith? Of course not just accepting some facts such as that Jesus is the Son of God and that He died and rose from the dead. Even demons believe these (Jas.2:19). But to receive salvation through God's unmerited favour towards us we must first know and believe that we don't deserve His favour. This is the conviction of our sins and sinfulness. If this conviction is genuine there will also be a resulting cry wanting to be saved from our sins. It is only then that we value the fact that God sent His Son to die in our place so that He could forgive our sins. In other words, faith that doesn't include conviction of sins and repentance is incomplete. Repentance is not 'works' as some accuse, but only the proper response towards God in order to receive His grace.
Once we are born again through the work of the Holy Spirit who gives us a new heart and writes His laws on our heart (He.8:10). This will give us a strong desire to keep God's commandments and our life will change (Jas.2:22). We don't do this in order to find acceptance from God, but as a result of His accepting us freely! If we say we are saved by grace and after that we start including something else in our thinking that what we do will win us favour from God, we go back under the law (Ga.5:1,2). Our standing with God is based only on grace.