Grace and truth came through Jesus Christ (cf. John 1:14). God's aim was to show the incomparable riches of His grace (cf. Eph. 2:7). God's grace is sufficient for us too, as His power is made perfect in weakness and the more sin abounds, the more grace abounds (cf. 1 Cor. 12:9; Romans 5:20). We cannot limit or exhaust the grace of God--it's infinite. This means we cannot pay it back, we do not deserve it, we cannot earn it, and we are not worthy of it. We owe an eternal debt of gratitude to the Lord.
We may think we contributed something to our salvation, namely faith, but faith is the gift of God and we were not elected because God foresaw grace, but God elected us unto faith it is also a gift, and also our righteousness is not our gift to God, but His gift to us. (cf. Isaiah 45:24). God's grace is never-ending and permanent once we acquire it through faith as the instrumental means. It is necessary for we cannot gain the approbation of God but must lean on His provision of grace as sufficient. We are to continue in God's grace and not to frustrate it (cf. Gal. 2:21), fall from grace when we try to be righteous by the deeds of the Law (cf. Gal. 5:4), be presumptuous and do great sin (cf. Psalm 19:13), or to take advantage of it and test God's patience by falling into carnality or continued sin.
Only God can change our nature and He does so from the inside out to make us new creatures in Christ (cf. 2 Cor. 5:17). Grace does abound to the chief of sinners(cf. 1 Tim. 1:15) and grace reigns (cf. Romans 5:21) or is sovereign and efficacious for the work required and salvation is a given. We must abide in the grace of God because we are works in progress as we work out our salvation with fear and trembling. (cf. Phil 2:12). We must not take grace as a given, though, and assume that God is obliged to show it (then it would be justice) or God is also just and holy and will punish His wayward children for their sins to get them back on track. But He gives more grace (cf. James 4:6). We are thus the stewards of the grace of God (cf. 1 Pet. 4:10).
It is important that we are not under the Law but under grace (cf. Romans 6:14). We are subject to a higher law, the law of love, and obey not in the written code of the Law (cf. 2 Cor. 3:3), but in the Spirit. Anyone who tries to justify himself by the works of the Law is under a curse (cf. Gal. 3:10). This is why we testify of the good news of the grace of God for grace is the love of God stooping to us in unmerited favor or undeserved blessing. Of His fullness, we have received and grace upon grace (cf. John 1:16). We must never think we were saved by favoritism or that we were any better or worthy than one who is lost, but God chose us according to His foreknowledge, good pleasure, and will. (cf. Eph. 1:5,11).