I believe we’re prone to fall into one of two basic soteriological errors:  “It doesn’t matter how I live since I’m forgiven.”  “If I don’t behave then I won’t be saved.” Those who’ve grasped God’s eternal salvation don’t think either way.
The key is in what God means when He says, “By grace you are saved.” (Ep 2:8) If we’re confusing grace with mercy, leniency, getting off easy, we miss His intent. Grace and mercy aren’t the same; they’re quite different.
We start out presuming salvation’s up to us, not God, and that’s where we go wrong. From that wrong place someone lies to us about what we need to do to finally end up in Heaven. Maybe some ritual called “accepting Christ,” and/or a certain behavior pattern that’ll be good enough for God. But it’s all wrong, because we’re starting at the wrong place.
Salvation isn’t up to us; it’s entirely in God’s hands. We’re born dead in sin (Col 2:13), enemies of God (Col 1:21), alienated from His life. (Ep 4:18) A dead man can’t do anything to raise himself; he can’t even want it. We need supernatural power; a miracle.
That’s where grace comes in: grace is “divine influence upon the heart and its reflection in the life.” (Strong) It’s God’s power intervening in our deadness (Ep 2:5), divine life energizing human life (1Co 15:10), conforming us to the image of Christ. (Ro 8:29)
The very desire to seek after God actually comes from God (Php 2:13); finding this within should encourage us to pursue Him until we find Him (He 11:6), relentlessly asking Him to quicken us … until He actually does. We can’t afford to settle for anything less. (Mk_8:36)
Grace is God choosing us (Ep 1:4), enabling us to seek Him and find Him (1Co 1:30), to obey Him, to hunger and thirst after righteousness, to have faith (Ep 2:8), to know that His promises are true, that He’s faithful.
We can have a relationship with God where:  He’ll never impute sin to us, crediting us with a perfect righteousness for Christ’s sake that’s independent of how we live (Ro 4:6-8), and  where He’s conforming us into His image (2Co 3:18), to live according to His way. How we live is evidence of His sanctifying work (Php 1:6), so it does matter; yet the saved don’t worry about losing salvation because it’s His work, not ours. (Ep 2:10)