The Old and New Testaments of the Bible repeatedly tell us that we need to repent of our sin and to accept and receive God's Savior, His Messiah, the Holy One of God, of which there is only one, as He says in Isaiah 45.
In Isaiah 51 and Isaiah 55, God says that His salvation comes only through one source, to which He sometimes refers as His "arm" or "arms", referring to the, then, forthcoming physical embodiment of His Messiah on Earth who would live and work among humanity. In the Old and New Testament times, before there were ever any "Christians" there were many people among the Jews, and among other people and nations around the world, who looked for the coming of God's Redeemer, as we see in Matthew Chapters 1 through 3 and in Luke 1 through 4.
In Matthew 7, Luke 13, and John 14:6, Jesus very pointedly addresses all those who would try to find another way to pay for, avoid admitting, or excuse their sin, or who might seek to work their way, around Christ, to God (which cannot be done unless one obeys and performs absolutely 100% of every single rule and function of God's Law everywhere and always). Why did Jesus state all that so exclusively? Because, as God in the flesh (also see Isaiah 7 and 8), He already set the perfect plan of redemption in place before the world was ever made; because He always knew that we human beings would need to be saved from our sin and our sinful choices.
Finally, all the scriptural promises were fulfilled that ushered in Jesus Christ (God's Messiah for which the world had been watching for thousands of years). As THE Messiah, in Luke 16:19-31, Jesus very pointedly warns both rich and poor alike of the coming shock that some will experience (after they die) about the exclusivity of God's salvation, that it is a one lifetime offer, never to be repeated to each human being. We get one opportunity right here and right now, to choose to repent of our sin before God, and then in faith to accept and receive the only Christ that God already foretold, and has already sent, to redeem us. IF we reject or neglect His offer then we have no one to blame but ourselves for the eternal suffering that we shall bring upon ourselves.
On the other hand, IF we elect and choose to repent of our sin and believe on and receive Jesus Christ by faith, then we have only Him to thank for making the way of salvation possible for us. Because we are not good (see Psalms and Romans), what every single one of us deserves is to spend eternity in torment, first in Hell until the Last Judgment, and then be cast into the Lake of Fire in eternal damnation. What God offers us in Jesus Christ is life eternal, under the blood of Christ, free in Him to learn and grow in our obedience to God in Christ Jesus. Because of our "repentance toward God and faith toward the Lord Jesus Christ", we are gifted by God, welcomed into His family, sealed with His Holy Spirit for eternity, and given a home of peace and joy with Him forever.
Reading the first three chapters of Genesis, from the very beginning of humanity, we can clearly see that God has offered His guidance and exclusive redemption to human beings. Thusly, God has manifested Himself throughout all Creation for every observant and concerned soul to see. The choice is up to you and me where we spend our eternal lives, in Heaven with Jesus, rejoicing in His fellowship and presence, or without Christ, by ourselves, in torment in the Lake of Fire. Religion or religiosity are NOT the solution. Besides the holy purchase price of our souls, which was the sinless blood and life of Jesus, God's Christ, no one else can buy our way into God's family or kingdom. Please choose God's only Savior and His only plan of salvation before it's too late.