The bible is easy to understand provided we approach it with an open mind. One text of scripture some who argue against man's responsibility after salvation don't like to read is our opening text.

Before salvation, no good works could save man. The only thing required for salvation was for man to put his faith in the finished work of Christ on the cross. Salvation is not a reward for being good( Eph 2:8-9). It is the gift of God.

However, after coming to Christ, man has a role to play so that he won't lose what he has received.  The opening text of scriptures makes clear man's role or duty in staying eternally secured. Let's consider the things Peter taught on that subject.

2 Peter 1:5-8

[5] And beside this, giving all diligence, add to your faith virtue; and to virtue knowledge; [6] and to knowledge temperance; and to temperance patience; and to patience godliness; [7] and to godliness brotherly kindness; and to brotherly kindness charity. [8] For if these things be in you, and abound, they make you that ye shall neither be barren nor unfruitful in the knowledge of our Lord Jesus Christ.

This is very clear. Apostle Peter tells us what we should add to our faith in Christ Jesus. He gave us a list of Christian virtues that should form or shape our conduct as believers. In verse 10, he says that doing these things( referring to the virtues he listed in previous verses), we will not fall away.

This is a clear indication that It is possible for a believer to fall away because staying in Christ and remaining eternally secured is predicated on doing the things prescribed in vs 5-8. Responsibility is conferred on man to do these things.

I love verse 11 which says, "Then God will give you a grand entrance into the eternal Kingdom of our Lord and Savior Jesus Christ". This is the bomb here.

Meaning that If we do the things prescribed in verses 5-8, that is when our entrance into heaven is guaranteed. You don't need a special knowledge or degree in theology to understand this. Read it again but prayerfully and meditatively.  Man is never without a role or responsibility.

Brethren, under grace, you have a role to play in your walk with God and it is not a hard one because his grace is available and sufficient. You don't need to be afraid of losing it or missing out, just abide in Christ so that his life can be expressed through you.