Angels are spiritual agents created by God to carry out His will. Ultimately, it is God who protects us, which (I assume) you would not have difficulty in accepting or understanding. As Jesus taught His followers to pray in the Lord’s Prayer, we are to ask God to “deliver us from evil.” Angels are sometimes the means by which He does this.
And He does this because there are multiple other agents, the devil and his angels; the fallen world in and through which they function; and our own fleshly, sinful natures that are always with us in this life, even after being saved, that are working just as purposefully to harm us or to lead us away from God.
Since angels are spirits, although they can assume visible form, we are usually not aware of their presence or functioning, but that doesn’t mean that they are not working to protect us in ways that we may never know or realize until eternity.
However, the presence and availability of these angels, or of God’s care and protection for us, for that matter, does not mean that we can foolishly or needlessly call on that protection without consequences. That is what the Bible, and Jesus Himself meant in saying, “You shall not put the Lord your God to the test” Deuteronomy 6:16, which was the verse that Jesus quoted back to Satan after Satan had quoted to Jesus the verse cited in the question in attempting to induce Jesus to throw Himself off the top of the temple in Jerusalem.
Jesus’ refusal to throw Himself down did not reflect a lack of faith on Jesus’ part, but was a response to the needless, foolish nature of the action that Satan was tempting Him to perform.
Jesus later showed His full confidence in the availability of God’s protection, which he willingly chose, however, not to use during His arrest in the Garden of Gethsemane when He told Peter to put away his sword after Peter had cut off the right ear of Malchus, the high priest’s servant, who was with the group that came to arrest Jesus.
Jesus said to Peter, “Do you think I cannot call on my Father, and He will at once put at my disposal more than twelve legions of angels? But how then would the Scriptures be fulfilled that say it must happen in this way?” Matthew 26:52-54.
Angels are ministering spirits sent to serve those who will inherit salvation! Hebrew 1:14.