So, God from the Old Testament is a completely different God from the New Testament. Sorry, but that is a laugh of Biblical proportions.
The God of the Old Testament is the God of the New Testament. What I'm saying is, the Jews and Muslims do not worship Him. They worship a god of their own manufacture, like you do.
The Old Testament served as a tutor to bring the world to Christ, through whom God offers eternal life.
(Gal 3:24-25 NKJV) 24 Therefore the law was our tutor [to bring us] to Christ, that we might be justified by faith. 25 But after faith has come, we are no longer under a tutor.
(Read Isaiah 53; Isaiah 11; Isaiah 9; Zechariah 4).
The Jews and Muslims reject Christ, the ONLY way to salvation. Therefore, they deny God and are consequently lost. (Tit 1:16 ESV) 16 "They profess to know God, but they deny him by their works. They are detestable, disobedient, unfit for any good work."
Regarding the Jews, the Jew Paul said, (Rom 10:1-3 NKJV) 1 Brethren, my heart's desire and prayer to God for Israel is that they may be saved. 2 For I bear them witness that they have a zeal for God, but not according to knowledge. 3 For they being ignorant of God's righteousness, and seeking to establish their own righteousness, have not submitted to the righteousness of God.