Regarding the issue of whether Christians have an “absolute” assurance of salvation, regardless of their actions, consider this warning Paul gave: “See then the kindness and the severity of God: severity toward those who have fallen, but God’s kindness to you, provided you continue in his kindness; otherwise you too will be cut off” (Rom. 11:22; see also Heb. 10:26–29, 2 Pet. 2:20–21).
17But if some of the branches were broken off, and you, being a wild olive, were grafted in among them and became partaker with them of the rich root of the olive tree, 18do not be arrogant toward the branches; but if you are arrogant, remember that it is not you who supports the root, but the root supports you. 19You will say then, “Branches were broken off so that I might be grafted in.” 20Quite right, they were broken off for their unbelief, but you stand by your faith. Do not be conceited, but fear; 21for if God did not spare the natural branches, He will not spare you, either. 22Behold then the kindness and severity of God; to those who fell, severity, but to you, God’s kindness, if you continue in His kindness; otherwise you also will be cut off. 23And they also, if they do not continue in their unbelief, will be grafted in, for God is able to graft them in again.
If you try anything other than God to gain Heaven you will be cut off. The other verses you cite, if read in context, will indicate the same.
It is about faith in Him. Not works.